i
Technical textile yarns
© Woodhead Publishing Limited, 2010
ii
The Textile Institute and Woodhead Publishing The Textile Institute is a unique organisation in textiles, clothing and footwear. Incorporated in England by a Royal Charter granted in 1925, the Institute has individual and corporate members in over 90 countries. The aim of the Institute is to facilitate learning, recognise achievement, reward excellence and disseminate information within the global textiles, clothing and footwear industries. Historically, The Textile Institute has published books of interest to its members and the textile industry. To maintain this policy, the Institute has entered into partnership with Woodhead Publishing Limited to ensure that Institute members and the textile industry continue to have access to high calibre titles on textile science and technology. Most Woodhead titles on textiles are now published in collaboration with The Textile Institute. Through this arrangement, the Institute provides an Editorial Board which advises Woodhead on appropriate titles for future publication and suggests possible editors and authors for these books. Each book published under this arrangement carries the Institute’s logo. Woodhead books published in collaboration with The Textile Institute are offered to Textile Institute members at a substantial discount. These books, together with those published by The Textile Institute that are still in print, are offered on the Woodhead website at: www.woodheadpublishing.com. Textile Institute books still in print are also available directly from the Institute’s website at: www.textileinstitutebooks.com. A list of Woodhead books on textile science and technology, most of which have been published in collaboration with The Textile Institute, can be found towards the end of the contents pages.
© Woodhead Publishing Limited, 2010
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Woodhead Publishing Series in Textiles: Number 101
Technical textile yarns Industrial and medical applications
Edited by R. Alagirusamy and A. Das
CRC Press Boca Raton Boston New York Washington, DC
Woodhead
publishing limited
Oxford Cambridge New Delhi
© Woodhead Publishing Limited, 2010
iv Published by Woodhead Publishing Limited in association with The Textile Institute Woodhead Publishing Limited, Abington Hall, Granta Park, Great Abington, Cambridge CB21 6AH, UK www.woodheadpublishing.com Woodhead Publishing India Private Limited, G-2, Vardaan House, 7/28 Ansari Road, Daryaganj, New Delhi – 110002, India www.woodheadpublishingindia.com Published in North America by CRC Press LLC, 6000 Broken Sound Parkway, NW, Suite 300, Boca Raton, FL 33487, USA First published 2010, Woodhead Publishing Limited and CRC Press LLC © Woodhead Publishing Limited, 2010 The authors have asserted their moral rights. This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information, but the authors and the publishers cannot assume responsibility for the validity of all materials. Neither the authors nor the publishers, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage or retrieval system, without permission in writing from Woodhead Publishing Limited. The consent of Woodhead Publishing Limited does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from Woodhead Publishing Limited for such copying. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. Library of Congress Cataloging in Publication Data A catalog record for this book is available from the Library of Congress. Woodhead Publishing ISBN 978-1-84569-549-1 (book) Woodhead Publishing ISBN 978-1-84569-947-5 (e-book) CRC Press ISBN 978-1-4398-3154-0 CRC Press order number N 10203 The publishers’ policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp which is processed using acid-free and elemental chlorine-free practices. Furthermore, the publishers ensure that the text paper and cover board used have met acceptable environmental accreditation standards. Typeset by Replika Press Pvt Ltd, India Printed by TJ International Limited, Padstow, Cornwall, England
© Woodhead Publishing Limited, 2010
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Contents
Contributor contact details
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Woodhead Publishing series in Textiles
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Part I Advances in textile yarn production 1
Introduction: types of technical textile yarn R. Chattopadhyay, Indian Institute of Technology, Delhi, India
3
1.1 1.2 1.3
3 4
1.10 1.11
Introduction Types of technical yarn Yarn characteristics: continuous filament, staple, core spun, plied/folded, cabled and braided yarns Yarn production: mono- and multifilament, tape, staple, core spun, folded and other yarns Characterization of yarn: dimensional parameters, packing of fibres and twist Structure of twisted yarn Properties and performance of technical yarns Properties of yarns: mono- and multifilament, tape, spun, wrap spun, core spun and plied/cord yarns Applications of mono- and multifilament, tape, core spun, plied and cabled yarns Market References
2
Advances in yarn spinning and texturising R. V. M. Gowda, V.S.B. Engineering College, India
56
2.1 2.2 2.3
Introduction to various yarn spinning technologies Compact spinning Rotor spinning
56 57 61
1.4 1.5 1.6 1.7 1.8 1.9
© Woodhead Publishing Limited, 2010
4 9 26 32 37 43 48 53 54
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Contents
2.4 2.5 2.6 2.7 2.8 2.9 2.10
Friction spinning Air-jet spinning Vortex spinning Core yarn spinning Wrap spinning Developing particular yarn properties Yarn texturising: technologies, developments and applications Future trends References
2.11 2.12 3
3.1 3.2 3.3
Modification of textile yarn structures for functional applications A. Das, Indian Institute of Technology, Delhi, India
67 70 72 74 80 82 85 89 89 91
3.4 3.5 3.6
Introduction Modifying textile yarn structures by bulking Modification of textile yarn structures by incorporating micro-pores Twistless and hollow yarns Future trends References
4
Yarn hairiness and its reduction A. Majumdar, Indian Institute of Technology, Delhi, India
112
4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9
Introduction Factors influencing yarn hairiness Yarn hairiness measurement Importance of yarn hairiness Modelling of yarn hairiness Yarn hairiness reduction Conclusions Acknowledgement References
112 113 117 122 125 128 137 137 137
5
Coatings for technical textile yarns A. Jalal Uddin, Ahsanullah University of Science and Technology, Bangladesh
140
5.1 5.2 5.3 5.4 5.5
Introduction Textile coating and laminating Coating formulations for technical textile yarns Coating polymers for technical textile yarns Choice of substrates for yarn coating
140 141 144 144 162
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Contents
vii
5.6 5.7 5.8 5.9 5.10
Principles of yarn coating Methods and machinery for yarn coating Applications and properties of some coated yarns Future trends References
163 170 176 182 183
6
Engineering finer and softer textile yarns J. Srinivasan, Kumaraguru College of Technology, India
185
6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8
Introduction: importance of finer and softer yarns Methods of engineering finer and softer yarns Structure of fine yarns Properties of fine yarns Applications Future trends Sources of further information and advice References
185 186 201 203 204 205 209 209 215
7
Assessing the weavability of technical yarns
B. K. Behera, Indian Institute of Technology, Delhi, India
7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8
Weavability of yarns Importance of weavability in industrial fabrics Factors influencing yarn weavability Warp breakage mechanism Analysis of warp breakage mechanism Evaluation of weavability Weavability of synthetic filament yarn Sizing of micro-denier yarns for achieving desired weavability Bibliography
7.9 8
8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8
Yarn imaging and advances in measuring yarn characteristics R. Fangueiro and F. Soutinho, University of Minho, Portugal Introduction Image processing techniques in fibrous material structures Yarn characterization Special advances in measuring yarn characteristics Online systems for measuring yarn quality Future trends Sources of further information and advice References
© Woodhead Publishing Limited, 2010
215 216 216 221 223 223 226 229 230 232 232 235 236 245 247 254 254 255
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Contents
Part II Types of technical yarns 9
Novel technical textile yarns
259
A. Jalal Uddin, Ahsanullah University of Science and Technology, Bangladesh
9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8
Introduction Reflective yarns UV protected yarns Metallic and metalloplastic yarns Antimicrobial yarns Yarns for specific purposes Future trends References
259 259 266 273 282 287 292 293
10
Electro-conductive textile yarns M. Latifi, P. Payvandy and M. Yousefzadeh-Chimeh, Amirkabir University of Technology (Tehran Polytechnic), Iran
298
10.1 10.2 10.3 10.4 10.5 10.6
Introduction Manufacture and structure of electro-conductive yarns Measurements Applications Future trends References
298 299 309 313 316 326 329
11
High modulus, high tenacity yarns
H. Hu and Y. Liu, The Hong Kong Polytechnic University, Hong Kong
11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9
Introduction Glass fibers and yarns Carbon fibers and yarns Ceramic fibers and yarns Basalt fibers and yarns Aramid fibers and yarns High-performance polyethylene (HPPE) fibers and yarns Sources of further information and advice References
329 330 345 360 365 370 378 382 384 387
12
Hybrid yarns for thermoplastic composites
R. Alagirusamy, Indian Institute of Technology, Delhi, India
12.1 12.2
Introduction Types of hybrid yarns
© Woodhead Publishing Limited, 2010
387 389
Contents
12.3 12.4
ix
400
12.5 12.6 12.7 12.8 12.9
Characterization of hybrid yarns Manufacture of thermoplastic composites with hybrid yarns Compaction and consolidation of hybrid yarns Hybird yarn structure – composite property relations Potential application areas of thermoplastic composites Trends in thermoplastic composite applications References
13
Shape memory polymer yarns
429
405 407 413 421 422 426
T. Wan, Nanjing University of Information Science and Technology, P. R. China
13.1 13.2 13.3 13.4 13.5 13.6 13.7
Introduction Thermo-mechanical behaviour of shape memory polymers (SMPs) Manufacture of shape memory polymer (SMP)-based yarns Applications Future trends Conclusion References
429
452
431 434 437 444 448 448
14
Plasma-treated yarns for biomedical applications
B. Gupta, S. Saxena, N. Grover and A. R. Ray, Indian Institute of Technology, Delhi, India
14.1 14.2 14.3 14.4 14.5
Introduction Chemistry of plasma processing Biomedical applications Conclusions References
452 457 468 487 488 495
15
Technical sewing threads
R. S. Rengasamy and S. Ghosh, Indian Institute of Technology, Delhi, India
15.1 15.2 15.3 15.4
Introduction Industrial sewing threads Surgical threads/sutures for medical applications References
495 495 513 532 534
16
Biodegradable textile yarns
S. Mukopadhyay, Indian Institute of Technology, Delhi, India
16.1
Introduction: principles and importance of sustainable yarns © Woodhead Publishing Limited, 2010
534
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Contents
16.2 16.3 16.4 16.5 16.6 16.7 16.8
Fibres from biodegradable polymers of natural origins Spinning of PLA polymers Electrospinning Fibres from biodegradable polymers from mineral origins Applications of biodegradable fibres/yarns Conclusion References
17
Yarn and fancy yarn design using three-dimensional computer graphics and visualisation techniques W. Tang, University of Teesside, UK and T. R. Wan, University of Bradford, UK
17.1 17.2
536 537 548 551 560 564 565 568
568
17.6 17.7
Introduction 3D computer graphics and visualisation technologies for cloths and yarns Microstructures of yarns and fancy yarns Mathematical modelling of yarn and fancy yarn structures Descriptions of a computer aided design (CAD) system for yarn and fancy yarn structures Conclusion References
Index
586
17.3 17.4 17.5
© Woodhead Publishing Limited, 2010
570 573 573 579 583 585
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Contributor contact details
(* = main contact)
Chapter 1
Chapter 4
R. Chattopadhyay Department of Textile Technology Indian Institute of Technology, Delhi New Delhi 110016 India
A. Majumdar Department of Textile Technology Indian Institute of Technology, Delhi New Delhi 110016 India
E-mail:
[email protected]
E-mail:
[email protected]
Chapter 2
Chapters 5 and 9
R. V. M. Gowda V.S.B. Engineering College NH 67, Covai Road Karudayamplayam P.O. Karur – 639 111, Tamil Nadu India
Ahmed Jalal Uddin Department of Textile Technology Ahsanullah University of Science and Technology Dhaka 1208 Bangladesh E-mail:
[email protected]
E-mail:
[email protected]
Chapter 6
Chapter 3 A. Das Department of Textile Technology Indian Institute of Technology, Delhi New Delhi 110016 India
J. Srinivasan Kumaraguru College of Technology Coimbatore 641 006 India E-mail:
[email protected]
E-mail:
[email protected]
© Woodhead Publishing Limited, 2010
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Contributor contact details
Chapter 7
Chapter 11
B. K. Behera Department of Textile Technology Indian Institute of Technology, Delhi New Delhi 110016 India
Dr Hong Hu* and Mr Yanping Liu Institute of Textiles and Clothing The Hong Kong Polytechnic University Hung Hom Kowloon Hong Kong
E-mail:
[email protected]
E-mail:
[email protected] [email protected]
Chapter 8 Dr R. Fangueiro* and F. Soutinho Department of Textile Engineering University of Minho Campus de Azurém 4800-058 Guimarães Portugal E-mail:
[email protected]
Chapter 12 R. Alagirusamy Department of Textile Technology Indian Institute of Technology, Delhi New Delhi 110016 India E-mail:
[email protected]
Chapter 10 Professor M. Latifi*, Dr P. Payvandy and Dr M. Yousefzadeh-Chimeh Department of Textile Engineering Textile Research and Excellence Centers Amirkabir University of Technology (Tehran Polytechnic) Hafez Avenue Tehran 15875-4413 Iran
Chapter 13 Dr T. Wan School of Maths and Physics Nanjing University of Information Science and Technology Nanjing 210044 P. R. China E-mail:
[email protected]
E-mail:
[email protected] [email protected] [email protected]
© Woodhead Publishing Limited, 2010
Contributor contact details
Chapter 14
Chapter 17
Dr B. Gupta*, S. Saxena, N. Grover and A. R. Ray Department of Textile Technology and Centre for Biomedical Engineering, Indian Institute of Technology, Delhi New Delhi 110016 India
Dr W. Tang* School of Computing University of Teesside Middlesbrough Tees Valley TS1 3BA UK
E-mail:
[email protected]
Chapter 15 Dr R. S. Rengasamy* and Dr S. Ghosh Indian Institute of Technology, Delhi New Delhi 110016 India
E-mail:
[email protected]
T. R. Wan School of Informatics University of Bradford Bradford West Yorkshire BD7 1DP UK E-mail:
[email protected]
E-mail:
[email protected]
Chapter 16 Dr S. Mukopadhyay Department of Textile Technology Indian Institute of Technology, Delhi New Delhi 110016 India E-mail:
[email protected]
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Woodhead Publishing Series in Textiles
1 Watson’s textile design and colour Seventh edition Edited by Z. Grosicki 2 Watson’s advanced textile design Edited by Z. Grosicki 3 Weaving Second edition P. R. Lord and M. H. Mohamed 4 Handbook of textile fibres Vol 1: Natural fibres J. Gordon Cook 5 Handbook of textile fibres Vol 2: Man-made fibres J. Gordon Cook 6 Recycling textile and plastic waste Edited by A. R. Horrocks 7 New fibers Second edition T. Hongu and G. O. Phillips 8 Atlas of fibre fracture and damage to textiles Second edition J. W. S. Hearle, B. Lomas and W. D. Cooke 9 Ecotextile ’98 Edited by A. R. Horrocks 10 Physical testing of textiles B. P. Saville 11 Geometric symmetry in patterns and tilings C. E. Horne 12 Handbook of technical textiles Edited by A. R. Horrocks and S. C. Anand 13 Textiles in automotive engineering W. Fung and J. M. Hardcastle 14 Handbook of textile design J. Wilson 15 High-performance fibres Edited by J. W. S. Hearle
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16 Knitting technology Third edition D. J. Spencer 17 Medical textiles Edited by S. C. Anand 18 Regenerated cellulose fibres Edited by C. Woodings 19 Silk, mohair, cashmere and other luxury fibres Edited by R. R. Franck 20 Smart fibres, fabrics and clothing Edited by X. M. Tao 21 Yarn texturing technology J. W. S. Hearle, L. Hollick and D. K. Wilson 22 Encyclopedia of textile finishing H-K. Rouette 23 Coated and laminated textiles W. Fung 24 Fancy yarns R. H. Gong and R. M. Wright 25 Wool: Science and technology Edited by W. S. Simpson and G. Crawshaw 26 Dictionary of textile finishing H-K. Rouette 27 Environmental impact of textiles K. Slater 28 Handbook of yarn production P. R. Lord 29 Textile processing with enzymes Edited by A. Cavaco-Paulo and G. Gübitz 30 The China and Hong Kong denim industry Y. Li, L. Yao and K. W. Yeung 31 The World Trade Organization and international denim trading Y. Li, Y. Shen, L. Yao and E. Newton 32 Chemical finishing of textiles W. D. Schindler and P. J. Hauser 33 Clothing appearance and fit J. Fan, W. Yu and L. Hunter 34 Handbook of fibre rope technology H. A. McKenna, J. W. S. Hearle and N. O’Hear 35 Structure and mechanics of woven fabrics J. Hu 36 Synthetic fibres: nylon, polyester, acrylic, polyolefin Edited by J. E. McIntyre
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Woodhead Publishing Series in Textiles 37 Woollen and worsted woven fabric design E. G. Gilligan 38 Analytical electrochemistry in textiles P. Westbroek, G. Priniotakis and P. Kiekens 39 Bast and other plant fibres R. R. Franck 40 Chemical testing of textiles Edited by Q. Fan 41 Design and manufacture of textile composites Edited by A. C. Long 42 Effect of mechanical and physical properties on fabric hand Edited by Hassan M. Behery 43 New millennium fibers T. Hongu, M. Takigami and G. O. Phillips 44 Textiles for protection Edited by R. A. Scott 45 Textiles in sport Edited by R. Shishoo 46 Wearable electronics and photonics Edited by X. M. Tao 47 Biodegradable and sustainable fibres Edited by R. S. Blackburn 48 Medical textiles and biomaterials for healthcare Edited by S. C. Anand, M. Miraftab, S. Rajendran and J. F. Kennedy 49 Total colour management in textiles Edited by J. Xin 50 Recycling in textiles Edited by Y. Wang 51 Clothing biosensory engineering Y. Li and A. S. W. Wong 52 Biomechanical engineering of textiles and clothing Edited by Y. Li and D. X-Q. Dai 53 Digital printing of textiles Edited by H. Ujiie 54 Intelligent textiles and clothing Edited by H. Mattila 55 Innovation and technology of women’s intimate apparel W. Yu, J. Fan, S. C. Harlock and S. P. Ng 56 Thermal and moisture transport in fibrous materials Edited by N. Pan and P. Gibson 57 Geosynthetics in civil engineering Edited by R. W. Sarsby
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58 Handbook of nonwovens Edited by S. Russell 59 Cotton: Science and technology Edited by S. Gordon and Y-L. Hsieh 60 Ecotextiles Edited by M. Miraftab and A. R. Horrocks 61 Composite forming technologies Edited by A. C. Long 62 Plasma technology for textiles Edited by R. Shishoo 63 Smart textiles for medicine and healthcare Edited by L. Van Langenhove 64 Sizing in clothing Edited by S. Ashdown 65 Shape memory polymers and textiles J. Hu 66 Environmental aspects of textile dyeing Edited by R. Christie 67 Nanofibers and nanotechnology in textiles Edited by P. Brown and K. Stevens 68 Physical properties of textile fibres Fourth edition W. E. Morton and J. W. S. Hearle 69 Advances in apparel production Edited by C. Fairhurst 70 Advances in fire retardant materials Edited by A. R. Horrocks and D. Price 71 Polyesters and polyamides Edited by B. L. Deopura, R. Alagirusamy, M. Joshi and B. S. Gupta 72 Advances in wool technology Edited by N. A. G. Johnson and I. Russell 73 Military textiles Edited by E. Wilusz 74 3D fibrous assemblies: Properties, applications and modelling of threedimensional textile structures J. Hu 75 Medical textiles 2007 Edited by J. F. Kennedy, S. C. Anand, M. Miraftab and S. Rajendran 76 Fabric testing Edited by J. Hu 77 Biologically inspired textiles Edited by A. Abbott and M. Ellison
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Woodhead Publishing Series in Textiles 78 Friction in textile materials Edited by B. S. Gupta 79 Textile advances in the automotive industry Edited by R. Shishoo 80 Structure and mechanics of textile fibre assemblies Edited by P. Schwartz 81 Engineering textiles: Integrating the design and manufacture of textile products Edited by Y. E. El-Mogahzy 82 Polyolefin fibres: industrial and medical applications Edited by S. C. O. Ugbolue 83 Smart clothes and wearable technology Edited by J. McCann and D. Bryson 84 Identification of textile fibres Edited by M. Houck 85 Advanced textiles for wound care Edited by S. Rajendran 86 Fatigue failure of textile fibres Edited by M. Miraftab 87 Advances in carpet technology Edited by K. Goswami 88 Handbook of textile fibre structure Volume 1 and Volume 2 Edited by S. J. Eichhorn, J. W. S. Hearle, M. Jaffe and T. Kikutani 89 Advances in knitting technology Edited by K.-F. Au 90 Smart textile coatings and laminates Edited by W. C. Smith 91 Handbook of tensile properties of textile and technical fibres Edited by A. R. Bunsell 92 Interior textiles: Design and developments Edited by T. Rowe 93 Textiles for cold weather apparel Edited by J. T. Williams 94 Modelling and predicting textile behaviour Edited by X. Chen 95 Textiles for construction Edited by G. Pohl 96 Engineering apparel fabrics and garments J. Fan and L. Hunter 97 Surface modification of textiles Edited by Q. Wei
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98 Sustainable textiles Edited by R. S. Blackburn 99 Advanced fibre spinning Edited by C. Lawrence 100 Fire toxicity Edited by A. Stec and R. Hull 101 Technical textile yarns Edited by R. Alagirusamy and A. Das 102 Nonwovens in technical textiles Edited by R. Chapman 103 Colour measurement in textiles Edited by M. L. Gulrajani 104 Textiles for civil engineering Edited by R. Fangueiro 105 New product development in textiles Edited by B. Mills 106 Improving comfort in clothing Edited by G. Song 107 Textile biotechnology Edited by V. Nierstrasz 108 Textiles for hygiene Edited by B. McCarthy 109 Nanofunctional textiles Edited by Y. Li 110 Joining textiles Edited by I. Jones and G. Stylios 111 Soft computing in textiles Edited by A. Majumdar 112 Textile design Edited by A. Briggs-Goode and K. Townsend 113 Biotextiles as medical implants Edited by M. King and B. Gupta 114 Textile thermal bioengineering Edited by Y. Li 115 Woven textile structure B. K. Behera and P. K. Hari
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1
Introduction: types of technical textile yarn
R. C h a t t o p a d h y a y, Indian Institute of Technology, Delhi, India
Abstract: Yarns which are used for manufacturing technical textile products are known as technical yarns. These yarns are designed primarily to meet some technical requirements of a product. Yarns used for apparel are excluded. Technical yarns have been classified according to their structural form and the raw material used in their manufacture. A brief outline of the production techniques is given. Yarn geometry and response to tensile deformation are discussed. Properties expected from this structure and form are analysed. Application and market potential are also reported. Key words: technical yarn, technical textile, yarn spinning, yarn structure, yarn property.
1.1
Introduction
Textiles have been used for centuries to meet apparel and domestic needs. Uses of textiles in these two sectors are dominant even today. Textiles have also been used to meet various technical functions such as for ropes, sailing cloth, etc. Textile products whose primary objective is to meet some technical requirements or functions are termed technical textiles. Hence, traditional apparel and home textile products are outside the domain of technical textiles. With time, technical usage of textiles has been growing. The development of new fibres and new processing technology is widening the areas of application. Technical textiles have been categorized on the basis of their use in different sectors of the industry and termed agrotech, buildtech, geotech, hometech, indutech, packtech, meditech, sporttech, etc. [1]. The forms in which technical textile products are available are thread, tape, woven, knitted, braided, knotted and non-woven fabric. Of all these forms, only non-woven products are made straight from staple fibres or short natural fibres, whereas for the rest the basic raw material is yarn. The yarns used could be in two different forms: a twisted assembly of continuous filaments or staple fibres, or a parallel assembly of filaments. The yarns are interlaced or looped together to form woven, knitted, braided or knotted products. Sometimes, the slender filaments are first transformed into a bulky yarn and then used in this form in some applications.
3 © Woodhead Publishing Limited, 2010
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Technical textile yarns
1.2
Types of technical yarn
Technical yarns can be classified on the basis of ∑ ∑
source, i.e. raw material, or structure and form.
Depending upon the fibre used, they can be classified as natural or artificial, and tenacity-wise further into low, high and very high tenacity yarns (Fig. 1.1). Based on the fibre, the yarns can be designated as cotton, silk, nylon or polyester, Kevlar or carbon fibre yarns. Natural fibre yarns are mostly used in low load-bearing applications. Biodegradability is one of the most important factors favouring the use of natural fibres in many technical applications. Classification on the basis of structure and form is shown in Table 1.1. Yarns can be designated as filament, tape, spun, core spun, plied, braided, etc. It is possible that many yarns may have a dual use in both non-technical and technical applications.
1.3
Yarn characteristics: continuous filament, staple, core spun, plied/folded, cabled and braided yarns
The general characteristics of the yarns classified according to their structure and form are discussed below.
1.3.1 Continuous filament yarns A filament yarn could be of either monofilament or multifilament type.
Raw material
Artificial
Natural
Low tenacity
High tenancity
High tenacity
Very high tenacity
Cotton Wool Silk Jute
Flax Ramie Hemp
Nylon Polyester Polyethylene Polypropylene
Carbon Aramid Glass
1.1 Classification of technical yarns according to raw material.
© Woodhead Publishing Limited, 2010
Introduction: types of technical textile yarn
5
Table 1.1 Classification on the basis of structure and form Type
Structure
Filament Monofilament, smooth Multifilament, smooth Tape Flat Spun yarn Uneven surface, hairy Core spun yarn Distinct core and sheath Plied/cabled Combination of single/plied yarns Braided Combination of single yarns
Form Rod-like Twisted Untwisted Twisted Untwisted Twisted Core twisted or untwisted Sheath wrapped Twisted Interlaced
Monofilament yarn
1.2 Some fibre cross-sectional shapes.
Monofilament Technical monofilament yarn consists of a single, solid filament having a diameter in the range of 100–2000 mm (0.1–2.0 mm). The cross-sectional shape of the filament can be varied depending upon the end use (Fig. 1.2). It could be circular (Fig. 1.3(a)) or profiled (i.e. triangular, multilobal, serrated, oval, dog-bone), solid or hollow. The surface could be smooth or structured. A non-circular cross-section encourages wicking. The surface area of the fibre increases as the cross-sectional shape becomes more and more non-circular. Monofilaments have high bending rigidity and more resistance to abrasive damage. The diameter of the monofilament depends upon its application. Multifilament A multifilament yarn (Fig. 1.3(b)) is a bunch of thin continuous monofilaments of infinite length. The filaments are assembled together to form a coherent strand through incorporation of a nominal amount of twist known as producer’s twist. The cross-sectional shape of the filaments decides how closely the fibres can be brought together in the yarn. A non-circular cross-section
© Woodhead Publishing Limited, 2010
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Technical textile yarns
(a)
(b)
(c)
(d)
(e)
(f)
(g)
1.3 (a) Monofilament, (b) multifilament, (c) commingled yarn, (d) tape yarn, (e) fibrillated tape yarn, (f) spun yarn, (g) core spun yarn.
inhibits close proximity between the fibres in the yarn and hence bulky or voluminous yarns are produced from them. Porous polyester fibres with pore radii in the range of 5–1500 mm enable the fibre to absorb water and dry rapidly. Circular fibres promote closeness and therefore give the yarn a lean look. The yarns are smooth, compact, dense and uniform, with maximum fibre strength exploitation. Multifilament yarns are much more flexible than the equivalent monofilament yarns. Intermingled/commingled yarn This is essentially a filament yarn. However, instead of twist holding the fibres together, the filaments are intermingled or entangled in order to avoid their separation during processing. When filaments of the same type are entangled, the yarn is known as an intermingled yarn; and when filaments of two or more types, e.g. carbon and polyester, are mingled together, the yarn is known as commingled yarn. The yarn looks tight at the mingle points which are distributed at regular intervals along the yarn length (Fig. 1.3(c)). The mingle points hold the filaments together. Tape yarns A tape yarn is basically a thin, narrow, ribbon-like film produced from a synthetic polymeric material such as polyethylene, polyamide or polyester
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Introduction: types of technical textile yarn
7
(Fig. 1.3(d)). A flat polymeric sheet or film is sliced into a large number of narrow tapes 20–40 mm in width with a thickness of 60–100 microns for technical applications. A tape may be further split or fibrillated (Fig. 1.3(e)) mechanically to produce a regular network of interconnected fibres which gives it a multifilament yarn-like texture.
1.3.2 Staple yarns Spun or staple yarns are linear assemblies of short discontinuous fibres. Synthetic or natural fibres (cotton, wool, jute, coir, etc.) are used as raw material for these yarns (Fig. 1.3(f)). When synthetic fibres are used, they are cut into shorter lengths (staples) so as to make them compatible in physical dimensions to their natural fibre counterparts. This makes synthetic fibres processable on machines that were designed primarily for natural fibres. Furthermore, it makes them suitable for blending if necessary. The fibres are held together by twist or fibre/filament wrapping. Hence, the magnitude of the twist or wraps is the most important parameter for these yarns. The yarn surface shows a helical arrangement of fibres with a lot of projecting ends.
1.3.3 Core spun yarn Core spun yarns have a distinct core and sheath fibre assembly (Fig. 1.3(g)). This can be either elastic or non-elastic. Non-elastic core A filament (mono or multi) is placed at the core of the yarn and wrapped by staple fibres. Such a combination leaves the opportunity to select appropriate fibres for the core and sheath to suit a specific application. As an example the core could be a high tenacity fibre such as polyester, nylon, polyethylene, polypropylene, etc., in filament or staple fibre form, and the sheath could be cotton, FR viscose, wool or any synthetic fibre in staple or wrapped filament form. Elastic core The core is either a rubber thread or any other elastomeric filament such as spandex, lycra, etc. The core is usually 2–10% of the total yarn mass. It is surrounded by suitable staple fibres. The yarn combines the attributes of the individual components. Stretch and recovery from stretch are the two most important attributes for these yarns.
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Technical textile yarns
1.3.4 Plied/folded yarn Plied/folded yarns are assemblies of twisted single yarns (Fig. 1.4). Usually the twist imparted at the plying stage is opposite to that in the single yarn, i.e. it is S over Z. This gives an opportunity to produce a torque-balanced structure. Depending upon the number of yarns plied together, it is called 2-ply, 3-ply or multi-ply yarn. When forming plied yarn 70% of the twist present in the single yarn is employed. The resultant yarn becomes more uniform, less hairy, more stable and stronger than the equivalent single yarn.
1.3.5 Cabled yarn When several plied yarns are similarly brought together and twisted again in opposite directions, a cabled yarn is formed. Technical yarns are usually cable twisted in order to make a torque-balanced yarn with superior properties.
1.3.6 Braided yarn Braided yarns can be either tubular or solid (Fig. 1.5). Several yarns, typically 8–36, are interlaced at an angle to form the braided structure. The interlacement pattern could be plain or twill. The final thread is torquebalanced and shows no untwisting tendency when stretched. It is highly Yarn
Ply yarn
Ply yarn
1.4 Ply yarn and cord.
1.5 Braided thread.
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flexible and its elongation is less than that of the equivalent twisted yarns. Table 1.2 summarizes the characteristics of different yarns.
1.4
Yarn production: mono- and multifilament, tape, staple, core spun, folded and other yarns
A brief description of the production techniques of different types of yarn is presented here. Table 1.2 Characteristics of technical yarns Type
Sub-category
Structure and form
Characteristics
Filament Mono-filament Multifilament
Rod-like, solid or hollow Assembly of large number of filaments, textured or twisted
Strong and rigid, inflexible, smooth Strong but flexible
Tape Flat Fibrillated and twisted
Flat, ribbon-like having Strong, good cover, primarily length and smooth width Mesh-type structure, Strong, soft twisted ridges and round
Spun
Round, hairy, soft, twisted ridges, core– sheath
Ring, rotor, friction and wrap
Weaker than filament yarn, softer
Core spun Rigid/elastic core Spun in appearance, core filament at centre, extendable
Strong, soft feel, extension controllable by nature of core filament
Commingled Self and hybrid Entanglements, homogeneous filament distribution
Uniform distribution of filament in yarn crosssection, better impregnation by polymer matrix
Plied Spun/filament Similar to spun/ Round, more uniform and plied multifilament yarn, stronger than single yarn, round twisted spirals, higher abrasion rounder resistance, torque balanced Cabled Spun/filament Prominent twisted cabled spirals, hard Braided Hollow/core sheath
Round, more uniform and stronger than plied yarn, higher abrasion resistance, torque balanced
Obliquely interlaced Strong, smooth, flexible, yarn following a spiral torque balanced path, hollow or with filament core
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1.4.1 Mono- and multifilament yarn production Thermoplastic polymers such as nylon, polyester and polypropylene are melt spun into filaments (Fig. 1.6). The material is supplied in the form of small ‘chips’ into a silo. It is then transported to the hoppers of extruders. The chips are now conveyed forward by a screw and simultaneously heated to transform them into a molten polymer. The pressure generated by the screw along with the metering pump forces the molten polymer to pass through tiny holes of spinnerets to form thin fibrous strands. In some cases, the extruder may be directly connected to the chemical reactor which is producing the polymer. As the molten polymer emerges from the spinneret holes, it is solidified by cooling using cold air or gas. The filaments are then drawn in a cold (nylon) or a hot (polyester) state to orient the chain molecules to the required extent for imparting the desired physical and mechanical properties into the filaments. Throughout the process, the maintenance of the correct temperature, pressure, viscosity and rate of cooling within strict tolerance limits is highly critical for an acceptable quality of the product. The crosssectional shape of the fibres can be changed by changing the shape of the holes in the spinneret. If the spinneret possesses one single hole, a monofilament is produced. A multi-hole spinneret produces multifilament yarn.
1.4.2 Tape yarn production As already mentioned, tape yarn can be either flat or fibrillated (twisted or untwisted).
Molten polymer
Metering pump
Spinneret
Cold air
Drawing
Winding
1.6 Melt spinning.
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Flat tape yarn In principle there are two ways to produce tape yarns [2]. ∑ ∑
Cutting of undrawn film Stretching followed by cutting.
In the first method (Fig. 1.7), an undrawn flat polymeric film is cut into narrow strips by a bar having razor blades as cutting devices arranged in parallel or by circular knives mounted on a rotating shaft. The strips can be varied in width from 1 to 20 mm or greater and in thickness from 20 to 110 mm. This operation is followed by stretching to impart the necessary dimensions and properties to the tape. The cutting width (b) of the primary film (or the distance between the blades to be adjusted) and the resultant tape linear density (T) expected are based on the following formulae:
b = w × (stretch factor)½
T = w × d × 10 × r
where w = required final tape width (mm), d = tape thickness (mm) and r = tape density (g/cm3). In the second method, the flat film is first heat-stretched monoaxially to achieve the desired properties and dimensions (thickness) and then subsequently cut in a similar fashion by a razor blade bar to the desired width. The minimum tape width and thickness achievable by this technique are 1–2 mm and 15–20 mm respectively. Cutting prior to stretching shows a reduction in tape width and thickness. Pronounced orientation and higher anisotropy of strength show a higher
Cutting blade Film
Cut film
1.7 Tape yarn production.
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fibrillation tendency compared with film tape made by stretching from narrow film ribbon cut from primary film prior to stretching. Fibrillated tape yarn Fibrillated yarns are essentially produced through a process of splitting a flat tape (2 cm in width) into fine fibrils. There are several ways to induce fibrillation, i.e. to generate a network-like structure. A flat tape is split either chemo-mechanically or by mechanical actions, i.e. brushing, rubbing, bending, twisting, air jet or ultrasonic treatments, to produce a mesh structure. The splittability of the tape can be improved either by blending two incompatible polymers or through addition of some compounds to the polymer which introduce flaws or weak places in the film. Greater molecular attraction in the form of hydrogen bonding and dipole interaction increase transverse strength and hence ability to split. Various fibrillation techniques are as follows. Uncontrolled fibrillation ∑
Twist fibrillation: This is the simplest process of fibrillation. Twisting of highly stretched film tape to over 100 turns/m on a ring twister results in fine fibrillation. The shearing force due to twisting leads to shearing action resulting in the splitting of the structure. The cross-section of the fibrillated fibre segments varies in thickness and linear density. ∑ Twist jet fibrillation: An air stream (at 10–250 psi) at high speed hits the tape at an angle, causing the tape to fibrillate. The rotating air vortex also causes the yarn to be interlaced and twisted. ∑ Fibrillation by transverse forces: The tape is abraded between two rubbercoated rotating rollers, one of them oscillating in its axial direction. The to and fro movement of the oscillating roller exerts a transverse stress, causing the tape to split. ∑ Chemo-mechanical fibrillation: A compound that decomposes at or near the extrusion temperature, a soluble salt or an incompatible polymer is added to the polymer, which introduces randomly distributed inhomogeneities in the film. These act as weak spots during the drawing process, enhancing lengthwise splitting during subsequent stretching. Controlled fibrillation To have some control over the fibrillation process, controlled mechanical fibrillation can be carried out in three different ways, i.e. by a needle roller, by embossing or by a cutting technique. In needle roller fibrillation, an array of film tapes 2 cm wide and 100 mm
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thick are fed under tension to a fibrillation unit consisting of a rotating pinned roller and a rubber-coated pressure roller (Fig. 1.8). The rubber-coated pressure roller ensures proper penetration of the film by the needles of the fibrillated roller, which in turn produces a network-like structure in the tape. The characteristics of the network structure are governed by the fibrillation ratio, the diameter of the needle roller, the angle of incidence and contact between fibrillation roller and film, the film tension, the film thickness, the needle density, the arrangement of needles on the fibrillator (a straight row of pins or a sinuous wave-like arrangement), the distance between needles, the distance between needle rows, and the depth of penetration of the needles. The fibrillation ratio is defined as
Fibrillation ratio =
inlet speed of the film surfface speed of the fibrillated roller
In the embossing technique, grooves are introduced into an undrawn film along its length by a heated profiled roller during the extrusion process by a profiled die or after extrusion. During subsequent stretching, the film separates along the groove into separated filaments. By imposing a complex profile pattern into the film, a network-like structure can be produced during subsequent stretching. Slicing is performed using a fine sawtooth-like fixed cutting tool on an unstretched or stretched film. This results in the production of filaments of rectangular cross-section and uniform fineness (6–6.6 dtex). The process gives better uniformity of fineness of individual filaments. A finer filament linear density is difficult to produce by this technique.
1.4.3 Staple yarn production Staple yarns are produced from short staple fibres. A schematic of the process steps is shown in Fig. 1.9. The fibres are first opened, and cleaned if necessary, mechanically by a series of machines that can perform the task of opening
Pinned fibrillation roller
1.8 Fibrillation technique.
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Technical textile yarns Opening and cleaning
Carding
Drawing
Spinning
Roving preparation
Drawing
1.9 Spinning process steps.
and cleaning simultaneously. Subsequently these are transformed into a sliver (a thick linear assembly of randomly arranged fibres) by a process called carding. The sliver is quite thick, usually 100 to 500 times thicker in terms of mass per unit length compared to the final yarn. The sliver therefore needs to be attenuated so as to make it thinner. The attenuation is carried out in steps by a process called drafting and drawing till it reaches the dimension of the desired yarn. Care is taken to ensure that the drafting process does not introduce too much irregularity (mass variation) into the product. The only operation which is to be accomplished thereafter is to impart cohesion to this thin assembly of fibres using one of the following techniques: ∑ Twisting by ring, rotor or friction spinning machine ∑ Wrapping an external filament by parafil spinning machine. The technology of inserting twist and wrapping is discussed below. Twisting by ring spinning machine The twister consists of a circular ring and a tiny C-shaped wire called a traveller which can move freely on the ring. The ring acts as a circular track for the traveller. The spindle on which the bobbin is mounted is placed within the ring. The yarn path from the front drafting rollers to the bobbin through the lappet guide and traveller is shown in Fig. 1.10. Every rotation of the spindle causes the traveller to rotate on the ring along with the loop of the yarn between the lappet guide and the traveller. Each rotation inserts one twist into the yarn. The rotational speed difference between the traveller and the bobbin or spindle causes the yarn to wind on the bobbin as well. In a dynamic situation, as the thin attenuated ribbon of fibres emerges from the front roller, it is immediately converted into yarn due to the insertion of twist and simultaneously wound on the bobbin. The insertion rate of twist can be varied from 8000 to 24,000 rev/min. With a yarn delivery rate of 15 m/min, it can introduce twist in the range of 13–41 turns per inch (5–16
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Front drafting roller
Lappet guide
Yarn balloon
Ring
Traveller Bobbin
1.10 Ring spinning process.
turns per cm). The system is capable of producing yarns in the count range of 5–100 tex. Twisting by rotor and friction spinning machine In ring spinning the twisting and winding processes are inseparable. This limits the twisting rate beyond a certain limit and as a result the production speed is limited. To overcome this technological limitation rotor and friction spinning have been developed. With increased twisting rate in both systems, an increase in production rate follows. In rotor spinning, a sliver is fed to the system which is opened thoroughly by an opening roller having a large number of pins on its surface, and the separated fibres are introduced through a transport channel to the rotor. With every rotation of the rotor the fibres accumulate in the form of layers within the rotor. The take-up package rotates independently of the twisting device (Fig. 1.11). When a seed yarn from the take-up package is introduced into the rotor, it joins the accumulated fibre rings within the rotor groove and starts rotating along with the rotor. As a result the accumulated fibre ring gets twisted with every rotation of the rotor. The twisted fibre assembly is withdrawn immediately by the take-up rollers and is wound onto a bobbin. Friction spinning (Fig. 1.12) offers a unique opportunity to combine fibres arriving at the twisting point from two or three different sources. Two drafting systems (one of the roller and the other of the opening roller
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Technical textile yarns 10
11
6
13 7
9 12 8
5
3
1 4
2
1. 2. 3. 4. 5.
Presser and feed plate Trash duct Opening roller Opening roller clothing Fibre feed or transfer tube (air stream) 6. rotor bearing
7. 8. 9. 10. 11. 12. 13.
Doffing tube Feed sliver Fibre collection surface Doffing tube navel Drawing-off rollers Feed roller Yarn
1.11 Rotor spinning [3]. Drafting unit
Fibres Transport duct
High draft unit
Friction drum Sliver Filament
Yarn
Opening roller
Sliver
delivery roller
Friction drums
1.12 Friction spinning.
type) are placed perpendicularly to each other in close proximity to a pair of perforated friction drums that act as a twister. The roller drafting system is aligned along the axis of the friction drum and the opening roller drafting system is placed perpendicular to it. Usually one sliver is fed through the roller drafting system and five or six slivers (2.5–5.0 ktex) through the opening roller system. The slivers are opened thoroughly by the opening rollers
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and released into the transport channel. The airstream passing through the channel brings the fibres to the torque field created at the nip of the rotating friction drums. The drum moves slowly in comparison to the speed of the approaching fibres. This causes fibres to accumulate at the torque field and to be made to stick to the drum surface by internal suction acting through the perforations of the drums at the nip. The drafted fibres from roller drafting also arrive at the nip. While passing through the nip, the fibres get twisted into a yarn by the torsion moment created on them by the two rotating drums. The fibres fed through the roller drafting system get false-twisted and remain in the yarn core, and those fed by the opening rollers get wrapped over it, and as result a distinct core sheath type of structure is produced. The yarn is withdrawn by a pair of rollers and led to the take-up package. Friction spinning is suitable for spinning very coarse count yarn and is capable of handling a wide variety of fibres of length 38–100 mm and fineness 0.6–3.3 dtex. Whenever necessary a filament can also be introduced through the nip of the front rollers in conjunction with or without the drafted assembly of fibres. This will cause the filament to occupy the centre part of the yarn. Usually the filament core imparts strength. This system thus offers enormous opportunity to produce different yarn structures through selective placement of fibres in different layers around the core and becomes extremely suitable for coarse count technical yarns. Filament wrapping A drafted ribbon of fibres is made to pass through a hollow tube which holds a rotating filament package (Fig. 1.13). As the package rotates the filament is withdrawn and passed to the tip of the hollow spindle. It joins the drafted ribbon of fibres and make wraps around the twistless stream of fibres which form the core. The percentage of filament varies from 1 to 5% of the ultimate yarn. The advantage of this system over ring spinning is that with the same fibre a finer yarn can be made, and coarser fibres can be used for a given yarn count. The count range of yarns that can be produced by various technologies is as follows: Technology
Count (tex)
Ring spinning Rotor spinning Friction spinning Wrap spinning
3–600 15–295 15–590 12–590
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Technical textile yarns High draft unit
Wrapping filament
Hollow spindle
Wrapped yarn
1.13 Wrap spinning.
1.4.4 Core spun yarns These yarns can be produced either on a normal ring spinning machine used in the cotton, worsted or jute industry or on rotor and friction spinning machines. Rigid yarn A strand of drafted staple fibres (called roving) is mixed with a pre-tensioned filament yarn at the nip of the front roller of the drafting unit, as shown in Fig. 1.14, and twisted together by a ring twisting device before finally winding onto a bobbin. The filament should be introduced at the centre of the drafted ribbon under a pre-tension (usually equivalent to 5% of the extension of continuous filament yarn) to ensure a true axial position of the filament so that it gets adequately covered by the staple fibres in the composite structure. When producing on a friction spinning machine, the filament yarn, under tension, is introduced by the front roller of the roller drafting unit between the nip of the twisting drums. If needed, a staple fibre assembly can also be
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Roving
1.14 Core spun filament yarn.
introduced into the core in a similar fashion by the roller drafting assembly. The core fibres remain in a false-twisted state within the twisted core spun yarn. Elastic yarn An elastomeric filament is introduced in this case. The filament, fed from a spool, needs to be stretched before entering the spinning zone. This action ensures elasticity in the final yarn when the core retracts, causing compacting and bulking of the spun yarn cover. The spool of the elastomeric yarn is fed by a positively driven feed roller system (Fig. 1.15). The spool rests on it and is driven by surface contact with the positively driven feed rollers. The stretch is adjusted by the speed of the feed roller in relation to the drafting roller speed. The elastomeric filament is extended by around 200–400% before being joined to the stream of drafted ribbon of fibres. The retraction percentage could be of the order of 116%. The core percentage can be worked out as follows [4].
Final core % =
TE K ¥ 100 DTC
Where TE = linear density of elastomeric yarn, K = correcting factor to modify the retraction fo spandex between front nip and traveller (usually 1.16), D = draw/stretch ratio and TC = linear density of final core spun yarn.
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Technical textile yarns Lycra spool
Positively driven feed roller
Drafted roving
1.15 Core spun Lycra yarn.
Elastic yarn can also be produced by the SIRO spinning technology. SIRO spinning is essentially a ring spinning system with an additional facility to introduce two rovings in the drafting zone instead of one. The drafted rovings before merging together at the spinning point remain separated throughout the draft field. The elastic filament is introduced at the nip of the front pair of rollers from behind. After twisting, the elastic filament remains in the core and the two drafted rovings wrapped around it ensure excellent core coverage.
1.4.5 Folded yarn production Most technical yarns are not used singly but are plied together to make them suitable for actual use. The yarns are twisted by an up- or down-twister, a two-for-one twisting machine or a combination machine. The traditional plying process consists of two operations, namely assembly winding and twisting. In assembly winding, the required number of single yarns (usually two) are wound onto an intermediate package (a flanged bobbin, cone or cheese). The bobbins are used as a feed package to the twister. Plied yarn Ring-twister/down-twister The assembled yarns are directed by a pair of rollers and guided to the twisting point consisting of ring and traveller. Rotation of the traveller causes a rotating balloon to be formed between the lappet guide and the ring. Every rotation of the traveller puts one turn into the yarn. As in ring spinning, the lag of the traveller causes the yarn to be wound on the bobbin. The ring
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rail keeps moving up and down in order to wind the yarn from bottom to top of the bobbin surface. The twist (T) inserted can be estimated from the following equation:
T =
ns n – 1 @ s v pdb v
where ns = spindle speed, v = delivery rate, and db = bobbin diameter at the point of winding. Usually Z-twisted single yarns are twisted in the S direction to form a snarl-free structure as the twists in single and double yarn balance each other. The yarn also becomes more uniform and round. Ring twisting is a downtwisting process. A twist ratio (folded/single) of 2/3 produces a balanced structure. High twist tyre cords are preferred to be twisted by ring twister. Up-twister In up-twisting (Fig. 1.16(a)) the supply package of suitable size is first formed and fixed on a spindle. As the spindle rotates at a constant speed a balloon gets formed and generates one turn in the yarn per revolution. The yarn is withdrawn at a constant rate and wound on a take-up package. The yarn passes through a flyer that rotates at a speed that is decided by the rate of yarn withdrawal and the bobbin diameter. The twist (T) inserted can be estimated from the following equation:
Delivery package
C
A Feed package Feed package
Spindle
B Spindle
(a)
(b)
1.16 (a) Up-twister; (b) two-for-one twister.
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T =
ns n + 1 @ s pdb v v
where ns = spindle speed, v = delivery rate, and db = bobbin diameter at the point of winding. The additional twist (1/πdb) is inevitable due to each turn around the bobbin and depends upon the bobbin diameter. This additional twist can be 10% of the total twist in the case of low twisted yarn (50–100 turns per metre). In both the up- and down-twister, either the feed or the delivery package needs to be rotated in order to insert twist at the intended speed. To minimize power consumption the rotating package needs to be smaller and slenderer. A consequent high power consumption puts a limit to the twisting rate. Besides, in both cases, a large yarn package is broken down into smaller ones. This necessitates further rewinding at a later stage to produce suitably sized packages. Two-for-one twister In the two-for-one twister, two twists get inserted in one revolution of the spindle. The feed package could be a conical, random or precision cross-wound assembly package. One or two packages (one above the other) is inserted on the spindle. The yarn enters axially into a central bore of the throw-off plate. The stationary feed package support is concentrically located. The yarn path from the supply package to the take-up package is chosen so that the yarn folds back on itself in the form of a loop (Fig. 1.16(b)). If the loop is now rotated, every rotation of the loop will insert one turn in the same direction in portions AB and BC successively. As a result, with the withdrawal of the yarn as the portion AB comes to the portion BC, these turns are added together to generate two turns per unit length in the final yarn. Cable yarns The production of cabled yarn is similar to that of plied yarn, but instead of twisting two individual yarns, two plied yarns are twisted together in opposite directions by another similar machine at the next stage. The cabled yarn can have an S-S-Z or S-Z-S, or a Z-S-Z or Z-Z-S twist combination at single, plied and cabled stage. These yarns are more uniform and stronger.
1.4.6 Intermingled/commingled yarn Intermingling of filaments is a substitute for twisting operations in which low twist is required to hold the filaments together [5]. The process is cheaper. Figure 1.17 shows a schematic of the intermingling/commingling process. In
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Air entry
Filament entry
1.17 Intermingling jet. Braid haul-off Braiding point
Anticlockwise
Carriers with spools
Clockwise
Serpentine tracks for carriers
Gear train below carrier for propulsion
1.18 Braiding process [6].
the commingling process, rapidly moving air in an air jet is used to generate entanglements among the filaments. Mingling of two or more yarns to form a single strand of yarn is defined as commingling. Commingled yarn consists of a blended combination of reinforcing filament yarn and filament yarn spun from thermoplastic polymers. The filaments remain scattered amongst one another at filament level in the final yarn. In the commingling process any weavable reinforcing fibre and most spinnable polymer fibres can be combined. Commingled yarn shows good processability by almost all known textile manufacturing technologies.
1.4.7 Braided yarn Many technical yarns are also produced by a process called braiding. In braiding several yarns interlace each other at an angle to form a braid. Bobbins containing the yarns are placed on the carriers (Fig. 1.18) which are moved
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Technical textile yarns
by rotating horn gears. As the gear rotates the bobbins move from one gear to the other and thus describe a serpentine path around a common axis. Half the carriers rotate in the clockwise direction and half in the anticlockwise direction. The interlaced structure is simultaneously withdrawn. The result is a structure of interlaced yarns following a spiral path. The interlacement can be of various types such as plain, twill, hopsack, etc. Depending upon the number of carriers and the braiding tension, a hollow circular braid or a ribbon braid or a tightly packed structure can be produced. If required, some other yarns can be introduced into the core to produce a core–sheath type of structure. High tenacity polyester may remain in the core, surrounded by a normal polyester, nylon, polypropylene, viscose or cotton braided sheath. A variety of yarns can be produced by having different ratios of core and sheath to suit different requirements.
1.4.8 Specialized yarns Conducting yarn Conducting yarns need conducting fibres. There are four methods to produce conducting yarn: ∑
Production of electrically conductive fibres by wet or melt spinning (conductive polymer polyaniline) ∑ Metallic fibre made from fine gauge copper, silver or nickel ∑ Coating or dyeing fibres with electrically conductive materials (metal powder, carbon black) ∑ Traditional core spinning technology using conductive fibre in the core covered by non-conducting sheath fibres. Such yarns are used in carpets, aircraft blankets, dry filtration, safety workwear, and upholstery. Melt and wet spinning ∑
Melt spinning: Conductive filler such as carbon black is incorporated into nylon or polyester polymer and extruded together through the spinneret to form the conducting fibre/yarn. Carbon content is limited to 40% as the mechanical properties of the polymer are adversely affected by a carbon content greater than 40% by weight. Conducting fibres are also produced by incorporating carbon nanofibres (CNF) or carbon nanotubes (CNT) into the polymer matrix and spinning them together. The nanotubes are dispersed in melt or liquid. ∑ Wet spinning: Xue et al. [7] suggested a wet spinning method as described below. An aqueous solution of PVA (polyvinyl alcohol) and purified
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CNT was prepared. The weight ratio of CNT was of the order of 40% for obtaining high conductivity. Stirring of the solution was continued at 60°C till uniformity and the required viscosity were obtained. A syringe pump immersed in a coagulating bath containing 17% sodium sulfate (Na2 SO4) extruded the PVA/CNT. The solution precipitated as gel and was guided towards a take-up roller. The important parameters that affected performance were the viscosity of the solution, the composition, concentration and temperature of the coagulating bath, and drawing during spinning. Coating/dyeing Incorporating metals in the yarns makes the yarn heavy, hence to overcome this problem metallic coating has been introduced. A yarn (natural or synthetic) is coated by a conducting metallic powder such as silver, copper or nickel. The substrate could be polyester, nylon filament yarn or cotton and wool yarn. According to Shaikhzadeh Najar et al. [8] the coating can be accomplished by three different methods: solution, vapour and mist polymerization techniques. These coated yarns have low conductivity. As an example a thin layer of copper sulfide is grafted on the surface of the fibre, making it a conductive fibre as well as imparting antibacterial properties. Xue et al. [7] passed cotton, silk, wool/nylon, polyester and polypropylene yarns through a solution of PVA/CNT, removed the excess material and dried it at ambient temperature overnight to get the yarns coated. Polyester multifilament yarns can be dyed directly by passing them through a dye bath containing the CNT-based dyestuffs [9]. The temperature is maintained at 40°C. A microwave vibration keeps the filament vibrating in order to dye the filaments thoroughly. The yarns are subsequently cured in an oven at 170°C for about 30 s. Spun yarn technology Polyester fibre embedded with carbon particles can be blended at 1% with normal polyester fibre to produce conductive yarn which can prevent discomfort from static in everyday clothing and carpets. A mixture of 2–5% is required for safety workwear and for industrial filters. Resistivity could be of the order of 1–100 MW/m2. Core spinning technology Using conductive material, e.g. stainless steel fibre (8 mm thick and 50 mm long) or wire (50 mm/140 den) in the core and polyester, FR viscose or cotton in the sheath, a core–sheath type conducting yarn can be produced
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Technical textile yarns
using friction spinning technology [10]. Various yarn constructions are possible with a core having conducting material in filament form and a sheath consisting of a mixture of conducting and non-conducting fibres in different sheath layers. In such constructions the outermost sheath layer is made of non-conducting fibres. The core/sheath ratio could be in the order of 30:70. Out of 70% sheath, 10–30% could be made of conducting staple fibres. The placement of conducting sheath fibres can be manipulated by adjusting the location of the slivers in the drafting unit.
1.5
Characterization of yarn: dimensional parameters, packing of fibres and twist
Technical yarns, like other yarns, can be characterized by their dimensional, structural and constituent fibre parameters. If special chemical treatments are applied to the yarn for specific purposes, this also needs to be mentioned. The various parameters required to characterize a yarn are suggested in Table 1.3.
1.5.1 Dimensional parameters Linear density/count Linear density or yarn count, yarn number and yarn size are indirect expressions of fineness of yarn. The fineness is not expressed by the yarn diameter because, firstly, the diameter is not stable and uniform along the yarn length in the case of spun yarn, and secondly, the cross-sectional shape may not be circular for both yarn and fibre. Hence it is indirectly expressed by either measuring the weight of a known length of yarn or measuring the length Table 1.3 Technical yarn characterization Parameters
Characteristics
Dimensional parameters
Linear density Diameter
Structural parameters
Twist and its direction Wrap density and its direction Number of plies, ply twist, and twist combination Core content, core–sheath ratio Blend constituents and blend ratio Packing coefficient
Constituent fibre parameters Number of filaments in cross-section Filament cross-sectional shape Length Linear density Crimp cross-sectional shape
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of a known weight of yarn. These two basic methods to express the linear density of any textile strand are known as the direct and indirect systems of expression. Therefore, by definition, the two systems of expression are:
Direct system = weight/unit length
Indirect system = length/unit weight
Generally the unit of weight is small and length is large so that reasonable figures are obtained in both systems to indicate fineness or linear density. In the direct system, the larger the indicated number of fineness, the coarser will be the yarn. In the indirect system it is just the opposite. Table 1.4 gives a comprehensive account of the units used in the expression of linear density. According to linear density, technical yarns can be divided into three categories: heavy industrial yarn (830–5500 dtex), light industrial yarn (50–550 dtex) and textile yarn (20–50 dtex). Linear density of plied yarn ∑
Direct system: In this system, the resultant linear density of plied yarn is the simple summation of the linear densities of the individual components, neglecting both yarn contraction and extension:
Resultant linear density, R = T1 + T2 + T3 + . . . + TN
where T1, T2, T3, . . . TN are the linear densities of the N individual components expressed in tex, den or jute. ∑ Indirect system: In the indirect system the relationship is
1 = 1 + 1 +...+ 1 R C1 C2 CK
where C1, C2 . . . CK are the linear densities of the K individual components expressed in any indirect system. It very often becomes necessary to convert linear density expressed in one system to another. The conversion factors are given in Table 1.5.
Table 1.4 Units of linear density System Direct Tex Denier Jute Indirect English Metric
Weight unit
Length unit
System unit
Gram (g) Gram (g) Pound (lb)
1000 metre (m) 9000 metre (m) 14,400 yard (yd)
g/1000 m g/9000 m
Pound (lb) Kilogram
Hank = 840 yard (yd) Hank = Kilometre (km)
Number of hanks/lb Number of hanks/kg
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Table 1.5 Unit conversion
Direct system
Indirect system
From
To tex
To denier
To jute
To English (Ne) To metric (Nm)
Tex (Nt) Denier (Nd) Jute (Nj) English (Ne) Metric (Nm)
1 0.11 Nd 34.45 Nj 590.5/Ne 1000/Nm
9.0 Nt 1 310 Nj 5315/Ne 9000/Nm
0.029 Nt 0.0032 Nd 1 17.14/Ne 29.02/Nm
590.5/Nt 5315/Nd 17.14/Nj 1 0.5905/Nm
1000/Nt 9000/Nd 29.02/Nj 1.693/Ne 1
Table 1.6 Specific volume of yarn Yarn
Specific volume (cm3/g)
Density (g/cm3)
Spun yarn Cotton 1.1 Nylon 1.45 Polyester 1.30
0.91 0.69 0.77
Filament yarn Nylon 1.35 Polyester 1.16
0.74 0.86
Yarn diameter It is at times necessary to know the approximate diameter of a yarn even though it is well known that yarn diameter cannot be estimated accurately owing to the highly compressible nature of the material. Diameter, however, gives an idea about the extent of cover achievable or the closeness of yarn packing in a fabric. Fabric thickness is also dependent on yarn diameter. The relationship between yarn diameter (dy) and linear density (C) can be worked out from the known experimentally determined values of specific volume (Vy). Such a relationship has been worked out by Hearle et al. [11]. The relationship between yarn diameter and yarn count (tex) is
dy = 2
Vy C C cm = 2 cm p ¥ 10 5 p ¥ 10 5 frf
where Vy = yarn specific volume, f = packing coefficient (see Section 1.5.2) and rf = fibre density (g/cm3). Therefore if the count and packing coefficient are known one can estimate yarn diameter. The value of the specific volume of yarn has been found to be mainly a function of twist, though fineness, crimp, flexural rigidity and length (for staple fibres) do have some influence. Some typical values of specific volume are shown in Table 1.6.
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Number of fibres/filaments in cross-section The number of filaments in a yarn is generally specified in the case of filament yarn. It can also be found by taking the ratio of yarn to filament linear density, i.e. N = 9C/nf where N = number of filaments/fibres, nt = yarn linear density (tex), and nf = fibre linear density (den). A filament yarn designated as 130/24 is of 130 denier fineness with 24 fibres or filaments in the cross-section.
1.5.2 Packing of fibres Since yarns are assemblies of fibres, it becomes important to know how the fibres are packed. Whenever a yarn encounters bending, twisting or tensile deformation, fibres are subjected to forces that cause them to move relative to each other. The ease of movement of fibres within a yarn depends upon how the fibres are packed within the yarn. While in some products a low packing density may be desirable, in others a highly packed structure is beneficial. The packing of fibres is objectively defined by the packing coefficient (f). This may be expressed in any of the following three ways. ∑
The ratio of the volume of the constituent filaments to the volume of yarn:
∑
f=
ry Vf or rf Vy
where Vf = fibre specific volume, Vy = yarn specific volume, rf = fibre density and ry = yarn density. The ratio of the total area of the constituent fibres to the area of the constituent fibres plus the area of voids within:
f=
nprf2 nprf2 + nV A
where n = number of fibres, nV = number of voids, A = area of void and rf = radius of fibre. ∑ The ratio of the sum of the area of the constituent fibres to the area of the yarn calculated from the average diameter of the yarn:
f=
npdf2 / 4 ndf2 Êd ˆ = 2 = nÁ f ˜ Ë dy ¯ pdy2 / 4 dy
2
where df = fibre diameter and dy = yarn diameter.
The fibres in a yarn, or the yarns or strands in a cord or rope, can be packed in two different ways, known as open and close packing (Fig 1.19).
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Open packing
Close packing
1.19 Open and close packing.
In open packing the fibres are arranged in successive concentric circles, while in close packing the fibres fit into a hexagonal pattern. The diameter of such an assembly of fibres can be described by the following equations [12]: Open packing Close packing Yarn diameter circumscribing the nth layer Number of fibres in the nth layer
(2n – 1)df ~2π(n – 1)
2(n – 1)df 6(n – 1)
For a close packed structure, the total number of fibres, S, in the crosssection is given by
S = 1 + (n – 1)/2[2 ¥ 6 + (n – 2) 6] = 1 – 3n + 3n2
For cord the same formulae will be applicable, except that the fibre radius should be replaced by the yarn/strand radius. Scardino [13] has suggested typical packing coefficients for a few yarns as shown in Table 1.7.
1.5.3 Twist Twist is defined as the number of turns present in a unit length of yarn. Twisting has the following purposes: ∑
To improve coherence between the fibres, though not really to improve the strength in filament yarn ∑ To improve both coherence and strength in staple fibre yarn ∑ To improve abrasion resistance and fatigue ∑ To enhance flexural rigidity ∑ To make the yarn compact ∑ To reduce snagging.
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Table 1.7 Packing coefficient of different yarns [13] Type of yarn
Packing coefficient (f)
Monofilament Tape Multifilament: Untwisted Regularly twisted Hard twisted Staple yarn Soft twisted: Hard twisted Ring Rotor Friction Wrap
1.00 1.00
S
0.25 0.60 0.90 0.33 0.60 0.50–0.60 0.35–0.55 0.30–0.55 0.40–0.70
Z
S twist
Z twist
1.20 Twist direction.
The twisting action causes the filaments to follow a helical path around the yarn axis. Twist is the most important structural parameter in a twisted yarn. In the case of multifilament yarns the twist is introduced primarily to bind the filaments together so that it facilitates processing by showing no fraying tendency. Besides processability and strength, twist also influences many other properties of yarn such as abrasion resistance, bending rigidity, fatigue resistance, etc. The twist level that maximizes one of the properties may not be right to maximize or minimize another. Hence, depending upon the end use, the optimum twist level has to be selected. The two most important aspects of twist is its direction and its level, i.e. intensity. If the surface helices are inclined from right to left it is known as Z twist (Fig. 1.20). The reverse is true for S twist. Usually twists in spun yarns are in the Z direction. In the single yarn stage, the twist direction does not influence the property of the yarn. Twist is usually expressed as twists per metre or twists per inch.
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In a plied structure, the ply twist direction is generally kept opposite to the single yarn twist direction. Twisting can give a balanced (torque-free) structure when an optimum level of ply twist is chosen with respect to the single twist. However, if the end use demands, ply twist in the same direction as the single twist can also be introduced. A plied yarn is usually designated by a number such as 30/4, meaning that four 30 single yarns have been plied together to form a single twisted structure.
1.6
Structure of twisted yarn
1.6.1 Geometrical relations Hearle et al. [11] derived the equations shown in Table 1.8 to describe the relationship between different geometrical parameters of a twisted yarn. However, these equations have been derived based on the following assumptions: ∑ Circular cross-section (Fig. 1.21) ∑ The fibres remain in a series of concentric cylinders of differing radii ∑ Each fibre follows a uniform helical path around one concentric cylinder ∑ The helix angle of the fibre path gradually increases from the centre to the outside as the twist/unit length is constant ∑ Constant density in fibre packing ∑ Large number of filaments in the yarn cross-section. Table 1.8 Equations showing relationship between parameters Equations
Parameters
Cylindrical coordinates h = 1/T l 2 = h2 + 4p2 r 2 L2 = h2 + 4p2 R2 tan q = 2p r/h tan a = 2p R/h = 2p RT
R = yarn radius r = radius of cylinder containing helical path of a particular fibre T = yarn twist (tpcm) h = length of one turn of twist (cm) a = surface angle of twist q = corresponding helical angle at radius r l = length of fibre in one turn of twist at radius r (cm) L = length of fibre in one turn of twist at radius R (cm)
Polar coordinates r = constant z = length along yarn axis z = hf/2p q = length of fibre along helical path q = z sec q = z [1+(r/R)2 + tan2 a]1/2 f = angular rotation of helix tan a = tan q (R/r) tpcm = turns/twists per cm
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r q
l h
l
h
q
q
z f 2pr
r
(b)
L
O
a
h a
L
(d) h
R (a)
2pR (c)
1.21 Idealized helical yarn geometry: (a) cylindrical model with (b) and (c) opened-up yarn at radius r and at yarn surface; (d) polar coordinates.
The various geometrical relations between the parameters of the yarns are shown in Table 1.6. The relation between the twist (T) and the helix angle (a) of a filament on the yarn surface is:
tan a = 2pRT = 0.0112 Vy CT = 0.0112 Vy t
where
t = CT = twist factor
For a given specific volume of yarn, the twist factor is proportional to tan a. Therefore the twist factor in a way represents the helix angle. Madsen et al. [14] reported that the average inclination angle (qmean) of the fibres in a twisted yarn is independent of the yarn diameter and depends only on the twist angle on the yarn surface. The expression for the mean twisted angle of fibres is:
q mean = a +
a – 1 tan 2 a tan a
However, for a twist angle less than 40°, the simple relationship has been shown to be
qmean = 0.695a
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Fibre torsion and bending within yarn The individual filament in a twisted yarn undergoes both torsion and bending deformation. According to Hearle et al. [15], the geometric torsion (tortuosity: t) and bending curvature (s) of a filament following a helical path with inclination angle q are given by
t = sin 2q = sin 2q 2r tanq /pT
where tan q = 2prT and hence
2 t = 2pT cos q
s=
2p sinq cosq sin 2 q or s = h r
where h = length of one turn of helix. As a result of twisting, the central fibre receives maximum torsion but experiences minimum bending, whereas the outermost fibre receives minimum torsion but experiences maximum bending. Yarn contraction/extension due to twisting/untwisting As a multifilament yarn is twisted it contracts in length. On the contrary if a twisted yarn is untwisted it increases in length. The ratio of the helical length (l) to the axial length (h) in one turn of twist is
l/h = sec q
The contraction factor (Cy), defined as the ratio of the untwisted to twisted yarn lengths or as the ratio of twisted and untwisted yarn count (direct system), is related to the surface helix angle by the following formula:
Cy = 1 seca 2
The retraction factor (Ry), defined as the fractional change in length with respect to the untwisted yarn length, is:
Êaˆ Ry = tan 2 Á ˜ Ë 2¯
1.6.2 Yarn stress–strain relation Hearle [16] derived the following formulae to relate fibre strain to yarn strain based on the assumption of idealized twisted yarn geometry:
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Introduction: types of technical textile yarn
For small strain: ef = ey cos2 q
For large strain: (1 + ef)2 = (1 + ey)2cos2 q + (1 – syey)2sin2 q
35
where ef = fibre strain, ey = yarn strain, sy = Poisson’s ratio and q = helix angle of the fibre at a given location in the yarn. The modulus of the twisted yarn and constituent fibre are related:
Ey/Ef = cos2 a
where Ey = yarn modulus, Ef = fibre modulus and a = helix angle of fibre on the yarn surface. All the geometrical parameters are in the unstrained state. The specific tension (fy) that a yarn will experience at any yarn extension ey can be given by: R
Ú(2prdr /V ) f (∂e /∂e ) y
fy =
0
f
f
y
R
Ú 2prdr /V
y
0
Considering Vy to be constant, l
Ú
(
)
fy = 2 ff ∂ef /∂ey t dt
0
where t = r/R, (R = yarn radius), ff = f (ef) and tanq = t tana. This equation can be solved to determine the yarn specific tension by knowing the equation of non-linear fibre stress–strain curve and other yarn geometrical parameters such as yarn radius, specific volume, twist angle, etc. For spun yarns Hearle suggests the following expression:
yarn strength yarn modulus = = cos2 a (1 – Kcosec a ) Fibre strength fibre modulus
where K is a factor that decreases with increase in fibre length, fineness and friction and with increasing migration.
1.6.3 Geometry of plied yarn Twist introduced in the plying process This model has been described by Treloar [17]. In plied yarn, the individual yarn axis is a twisted curve. The rate of rotation of the axis is known as the
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tortuosity of the curve. It is convenient to define the position of a filament in the yarn by the angle f (measured with respect to the principal plane of curvature of the strand axis at the point considered). The torsion with respect to the plane of curvature, t0, is:
t0 =
df dl
As the yarn axis is itself a helix having radius a and angle a, the tortuosity (1/S) is:
1 = sin2a = 1 sina cosa 2a S a
or
2pn cos 2 a
Therefore the total individual yarn torsion is given by
t = t 0 + 1/S =
df 1 l + sina cosa = 2 pn1 1 + 1 sina cosa dl a l a
where n1 = twist in individual yarn, l1 = length of individual yarn axis before plying, l = the corresponding length after plying, and a = helix radius of the yarn axis around the ply axis. The final torsion in the single yarn is obtained by adding the tortuosity of the ply axis to the initial yarn torsion taking into account the change in length of the individual yarn axis. The relation between the ply twist (N) and the ply helix angle (a) is:
tan a = 2paN
Usually the ply twist is opposite to the single yarn twist. The ply retraction initially reduces, attains a minimum and then increases again with increase in ply twist. This is due to the lengthening of individual yarns as they receive opposite twist at the beginning. The location of the minimum shifts to a higher ply twist level as the twist in the individual yarn increases. The retraction values increase as the yarns gets more and more inclined with increase in ply twist. Filament angle It is important to keep the filament angle parallel to the ply axis in any structure as it will protect the filaments from abrasion damage when the yarn moves longitudinally. For a two-ply yarn made from yarns of the same diameter (b) , the inclination angle (b0) for the outside filament with respect to the cord axis has been shown to be given by
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l 2 tana + bt 1ÊÁ 1 ˆ˜ Ël¯ tanb 0 = l 1 – bt 1ÊÁ 1 ˆ˜ tan a Ël¯
The filament angle (f0) measured with respect to the ply axis is
f0 = b0 – a
In order to make the outside filament parallel to the ply axis for a two-ply yarn, the relationship between single yarn and ply twist has been shown to be:
n1/N ≈ – 2
To keep the filament parallel with respect to the ply axis, the ply twist should be half of and opposite to the single yarn twist in the case of twoply yarn.
1.7
Properties and performance of technical yarns
Performance and properties are highly related. The product properties depend upon the properties of the raw material and the structural characteristics of the product. As an example, for fabric, the properties of its constituent yarns and the way the yarns have been assembled into the fabric are important. In order to understand the performance behaviour of technical textiles it is imperative to know the properties of the technical yarns. Since fibre is the basic raw material for technical yarns, the properties and performance of the yarn are highly influenced by the fibre characteristics and yarn structure. The fibre characteristics that affect performance are its dimensional, mechanical, chemical, electrical, thermal and absorptive characteristics.
1.7.1 Role of fibre parameters Fibre diameter Fibre diameter, density and fineness are related to each other. The linear density (i.e. fineness) of fibres used in technical textiles ranges from 2 to 7 denier. For microfibres it could be in the range of 0.1–0.3 denier. Monofilament could be of 15 denier. Assuming a cylindrical cross-section, it can be shown that
Filament diameter (df) = 11.89 ¥ 10 –4
w cm rf
where w = fibre linear density (denier) and rf = fibre density (g/cm3).
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Filament diameter therefore increases with fibre denier and decreases with density of the fibre. Yarns made from finer fibres will be compact and will hold less air between the fibre interstices. Finer fibres are flexible and as a result the yarn and corresponding fabric can be expected to be flexible too. Finer fibres produce finer capillaries, which would make wicking faster due to higher capillary pressure. Hence in sportswear sweat removal from skin is expected to be faster with finer fibres. A compact fabric made from microfibre can make the fabric waterproof, as water droplets cannot penetrate so easily through it. For a given yarn diameter, the yarn will be lighter if it is produced from a fibre of lower density. Similarly for a given yarn count the yarn will be bulkier if it is produced from a low-density fibre. Fibres having density less than 1.0 float on water. Hence for products that need to float on water polypropylene and polyethylene fibres need to be used. Fibre specific surface area The specific surface area of fibre, defined as the surface area per unit volume, affects heat and moisture transport and the twist requirement in spun yarn. The specific surface area is given by:
ˆ Ê r Spa = 2p2l = 2 = 2 Á 5.95 ¥ 10 –4 w ˜ = 3361.3 f cm 2 /cm 3 rf ¯ w Ë pr l r
where r = fibre radius (cm). The finer the fibre the greater will be the specific surface area. With an increase in density the specific surface area also increases, provided the fineness remains the same. More specific surface area means more possible area of contact between fibres and hence better cohesion and grip between fibres. Fibre bending rigidity The flexural rigidity (B) of a fibre or filament is dependent on a few fibre parameters as suggested by the following equation [18]:
2 B = SET ¥ 10 –3 4pr
where
2 S (shape factor) = 4 pk A
and E = tensile modulus (N/tex), T = linear density of filament (tex), r = filament density (g/cm3), k = radius of gyration and A = area of cross-section. © Woodhead Publishing Limited, 2010
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Hence, as the filament is made finer, it becomes more flexible and so would the yarn and fabric made out of it. The shape factor changes as the fibre becomes more and more non-circular. The fabric flexibility can be varied by the fibre/filament linear density. For stiff fabric monofilaments are used instead of multifilaments. The creasing tendency of the fabric increases as the fibre becomes finer. However, fabric abrasion resistance and resilience increase with coarser fibres. This is all due to the increased bending stiffness and strength of coarser fibres. Torsional rigidity Torsional resistance of fibres also increases rapidly with increase in linear density and shear modulus. Therefore a coarser fibre is more difficult to twist and once twisted stores a higher level of torsional strain energy than do finer fibres. This may manifest itself in a yarn in the form of snarls or kinks observed in twisted yarns. To suppress it, twist setting is practised in the industry. Torsional strain energy is released by steam setting, i.e. by exposing the yarn in a heated steam chamber. The following equation shows the torque required to produce T turns in unit length [19]:
torque =
ehC 2 T r
where e = shape factor, h = specific shear modulus, C = linear density, r = density and T = twist. With increase in fibre linear density, the torque requirement increases disproportionately. Fibre length Fibre length matters in the case of spun yarn. Use of long fibres in spun yarn reduces hairiness owing to the smaller number of terminating ends in a given section of yarn. Long fibres need less twist for optimum strength and yarns made from such fibres become soft. In filament yarns all filaments are of infinite length.
1.7.2 Technical fibre characteristics Mechanical properties Some fibre characteristics that have an important bearing on yarn properties are shown in Table 1.9. Natural fibres are in general weaker than synthetic fibres. Usually high modulus and high tenacity fibres are used in those areas where products made from these yarns are to carry loads or high impact forces.
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Fibre Density Fineness Diameter Melting point Tenacity Initial modulus (den) (mm) (°C) (N/tex) (N/tex) (g/cm3)
Breaking extension (%)
Manila (Abaca) 1.38 Sisal 1.38 23–406 0.1–0.46 mm Coir – 0.1–0.45 mm Flax 1.7–18 0.04–0.62 mm Hemp 3–20 0.16 mm Jute 1.5 13–27 0.03–0.14 mm Cotton 1.54 12–18
2.6 1.9 16.0 2–3 1–6 1–2 4–8
Nylon Polyester Polypropylene Polyethylene Aramid HMPE E glass Carbon
Chars at 150 – – – – – –
530 440 20 1.8 43 540 18–20 470 18–22 310 17.2 33 5
1.14 6–20 7–15 258 840 1.38 7–30 250–266 820 0.91 160–175 620 0.95 20 125–140 530 1.44 1.6 10–12 500, decomposes 200 0.97 1.6 14.5 150 3500 2.60 1.6 9 1500–2500 1.78 – – 2000–6000
7 11 7 4 60 100 29 180–450
15–28 12–15 18–22 20–24 1.5–3.6 2.7–3.5 4.8 0.7–2.0
Technical textile yarns
Table 1.9 Fibre properties
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A strong fibre will result in a strong yarn and in turn a strong tear-resistant fabric. The elongation of fibres is also extremely important, because together with tenacity it determines the shock-absorbing capacity of the product. Elastic elongation (the part of the extension that is recoverable) matters most in specialized products such as sportswear, elastic bands and technical products (ropes for mountaineering, bungee jumping, shock-absorbing nets, etc.). Recovery from elongation ensures dimensional stability after repeated use. High initial modulus indicates resistance to initial deformation and also, flexural rigidity of the yarn. Depending upon the level of performance required in a product, one has to choose the fibre or fibre combination and its proportion for a given product. Carbon fibre and glass fibre do not creep, and aramid fibres show little creep but creep is a serious problem for polyethylene and polypropylene fibres. Absorption property Natural fibres absorb a lot of moisture and as a result their properties can change significantly (Table 1.10). Yarns made from polypropylene, polyethylene and HMPE do not absorb any moisture, whereas those made from nylon and aramid will absorb moisture. The absorbance of moisture can lead to loss in strength in the case of nylon and wool, whereas for cotton and jute, strength increases. It can lead to an increase in fibre diameter and consequently of yarn diameter. This may lead to an increase in the hardness of natural fibre rope. The increase in yarn diameter may lead to a change in the permeability characteristics of the corresponding fabrics. Thermal behaviour Fibres react to heat in different ways. They may shrink, change colour, soften, become sticky, melt, decompose or carbonize. Fibres such as cotton Table 1.10 Moisture regain and relative strength [2] Fibre Moisture regain at Relative strength Diameter swelling 65% RH with respect to dry (%) strength (%) Polyester Polyamide (nylon) Polypropylene Polyethylene Aramid HMPE Cotton Wool Jute
0.5 100 4–5 85–95 0 100 0 105 1–7 95 0 100 7–8 100–110 14–15 70–90 13.8
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1.9–2.6 [16] 0 0
20 [16] 14.8 20
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have no melting point and char at very high temperatures (Table 1.11). Nylon and polyester, being melt spun, have fixed melting points. About 20–30°C below the melting point there is range of temperature in which they become soft and sticky and hence it is advisable not to come close to these temperatures. Below the softening region lies a broad zone where heat setting is possible. Heating and cooling in a given form results in the existing form being retained as the normal form to which the fibre tends to return when deformed. Cellulose fibre burns easily and quickly, leaving some ash. Acrylic fibres cannot be ignited so easily, but once ignited burn very fast. Polyester and polyamide are difficult to ignite; however, the fibre melts and drips. Only wool has the most favourable burning characteristics. It is difficult to ignite and after burning it leaves brittle ashes that quickly cool and do not adhere to human skin. Aramid and nomex are highly heat-resistant fibres and are therefore used for making yarns for firefighters’ protective clothing. Thermal conductivity Warmness and coolness are associated with thermal conductivity of the fabric which in turn is decided mainly by the bulk of the fibrous assembly, the thermal conductivity of the fibres and the surface roughness of the fibres or yarns or fabrics. The thermal conductivity of some fibres is given in Table 1.11 [20]. Polypropylene fibre has the lowest thermal conductivity whereas cotton has the highest. A fabric will show low thermal conductivity if it has high bulk, since the pores in it can hold a lot of air between the fibres, and air has a very low thermal conductivity (0.026 W m–2 K–1). The melting point limits the use of a fibre in a given environment.
Table 1.11 Thermal conductivity of different fibres Material
Melting point/degradation [3] (°C)
Thermal conductivity [19] (W m–2 K–1)
Air Cotton Wool Polypropylene Polyester Polyacrylonitrile Polyamide Aramid Nomex UHM polyethylene
– 150 (degrades) 132 (degrades) 165 260 150 (degrades) 215 (Nylon 6) 260 (Nylon 6.6) 427–482 430 144
0.026 0.461 0.193 0.117 0.141 0.200 0.243 0.130 – –
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Chemical and UV resistance While selecting fibre for a specific yarn, one should know in advance the response of the fibre to various environmental situations. A qualitative understanding can be of great help in choosing the fibre for a given application. Table 1.12 shows the resistance of fibres to various environments. HMPE fibre is found to be best suited for all environments. The final selection has to be based on the optimum combination of properties including mechanical, thermal and electrical properties.
1.8
Properties of yarns: mono- and multifilament, tape, spun, wrap spun, core spun and plied/ cord yarns
1.8.1 Monofilament yarn Monofilament yarns are stiffer than the equivalent multifilament yarns. Being stiffer gives rigidity to the structure. Having a lower surface to volume ratio, they pick up fewer contaminants than multifilament yarns. This makes the filter fabrics readily cleanable after use. Monofilament yarns offer greater transparency as light can easily pass through them. Monofilaments can have a variety of cross-sectional shapes such as circular, square, flat, rectangular, oval, hollow, etc. The cross-sectional shape affects lustre, covering power and hand. Circular monofilaments have a minimum surface area for a given linear density. Monofilament has greater resistance to in-plane abrasive wear. However, if the wear involves repeated bending, it may wear faster than multifilament yarn. Monofilaments also offer better surface release than multifilaments. Finish Monofilaments can be given suitable finishes such as flame retardant, antioxidants, pigments and thermal and UV stabilizers to enhance filament Table 1.12 Resistance of fibres to various environments Fibre
Resistance Abrasion resistance to UV Surface Internal
Acid resistance
Alkali resistance
Cotton Nylon Polyester Polyethylene HMPE Aramid Polypropylene
Good Good Excellent Fair Excellent Fair Fair
Poor Poor Good Excellent Excellent Poor Excellent
Very good Excellent Poor Excellent Excellent Very good Excellent
Poor Good Very good Fair Excellent Fair Good
Good Very good Excellent Good Excellent Good Good
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properties. Various additives are used to change surface properties, i.e. to make the yarns more or less wettable. Water-soluble monofilaments are made from polyvinyl alcohol.
1.8.2 Multifilament yarn Due to the presence of a large number of thin fibres (fibre diameter 10–50 mm), the flexural rigidity of multifilament yarn is much lower than that of an equivalent monofilament yarn. The covering power of multifilament yarn is better than that of monofilament yarn. In a woven structure at the interlacement points, multifilament yarn gets flattened and thereby produces a fabric with low thickness and smooth surface in comparison to monofilament fabrics. Fibres with a circular cross-section come closer to one another, making the yarn compact in appearance and also leading to the largest area of contact with any external surface. Fibres with non-circular cross-section are inhibited from close proximity within a yarn and hence bulky yarns are produced from non-circular fibres. A bulky yarn leads to a bulky fabric, which improves thermal resistance and makes it suitable for extremely cold climates. The properties of a multifilament single yarn can be manipulated through twist. Multifilaments have a larger surface area than the equivalent monofilament yarns and therefore adhere better with a matrix material or coating.
1.8.3 Tape yarn The linear density of a tape yarn may lie in the range of 16,500 to 27,500 dtex. The yarn is lustrous and strong, with large covering power. Fibrillated tape yarns offer a spun look. Fibrillation reduces bending rigidity and makes the yarn soft. Fibrillatability varies from fibre to fibre. Polypropylene shows a higher splitting tendency than polyethylene at the same molecular orientation. Polyamide and polyester show less splitting tendency. Greater molecular attraction in the form of hydrogen bonding between the molecules increases the transverse strength of these polymers.
1.8.4 Spun yarn Spun yarns, made of short natural fibres or staple cut synthetic fibres, are hairy and therefore not as slippery and smooth as filament yarn. If made from the same fibre, spun yarns may be weaker than an equivalent filament yarn. However, they have a higher elongation than filament yarn. The most important structural parameter that affects the properties of spun yarn is twist. With increase in twist, yarn strength first rises, then attains a maximum and declines thereafter (Fig. 1.22). For multifilament yarn it starts declining practically from the beginning. This rise and fall of strength has been ascribed
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Strength
Multifilament yarn
Spun yarn
Twist
1.22 Twist–strength relationship.
Table 1.13 Translation efficiency of various yarns Type of yarn
Translation efficiency (%)
Monofilament/tape Multifilament: Untwisted Slightly twisted Ring spun yarn: Soft twisted Hard twisted
100
Rotor Friction (dref-2) Wrap spun
30–55 (author’s data) 25–35 (author’s data) 25–60 (author’s data)
98 95 45 67
to the interaction between two opposite effects known as the obliquity effect (strength underutilization due to inclined placement of constituent fibres) and the diminishing slippage effect (due to greater transverse force due to helical configuration of fibres under tension). As a consequence an optimum is observed. The location of this optimum may vary from fibre to fibre, with length, fineness and frictional parameters. For multifilament yarn an initial rise in the low twist region is due to the mutual support that the filaments provide to each other due to frictional interaction between them which enhances with twist. The obliquity effect takes over quickly in the case of multifilament yarn. The strength translation efficiency that represents fibre strength utilization in yarn is highest for filament and tape yarns and usually less for spun yarns (Table 1.13).
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1.8.5 Wrap spun yarn The tenacity of wrap spun yarn depends not only on the core fibre tenacity and friction but also on the wrapping filament property and wrap density. With an increase in wrap density, the filament to fibre contact area increases, giving a higher radial force. Due to the increase in core fibre friction, the core fibres are restrained from slippage. As a result tenacity increases with the increase in wraps per metre (Table 1.14). Typical load–elongation behaviour of jute–polyester wrap spun yarns is shown in Fig. 1.23 [21]. The filament elastic modulus and fineness are also important in determining wrap yarn strength [22]. As the fibres in the core remain straight and parallel, the yarns are stronger than the equivalent ring yarn by around 30%. A higher wrap density can make the yarn stiff due to the increased packing of constituent core fibres which will hinder the free movement of fibres during bending.
1.8.6 Core spun yarn The properties of a core yarn can be engineered by selecting appropriate core and sheath fibres. By keeping a strong filament yarn in the core, the yarn can be made much stronger than equivalent conventional spun yarn. The modulus and strength of such yarn are manipulated through the properties of the core component. Similarly, through the use of an elastic core the yarn can be made into a stretch yarn, its stretchability being manipulated
Table 1.14 Typical properties of wrapped spun yarn [19] Yarn sample Wraps/m Tenacity Breaking Specific flexural Work of (g/tex) extension (%) rigidity (x 10–5) rupture (g.cm2) (g.cm2) Jute–polyester
200 220 240 260 280
10.19 11.51 11.93 12.00 12.39
2.00 2.75 3.66 4.03 4.36
2.11 2.20 3.27 3.15 3.53
968.1 1808.1 1845.6 2161.3 2045.0
Jute–nylon
200 220 240 260 280
8.57 8.84 10.6 10.3 11.4
3.39 3.64 4.19 4.89 5.38
1.90 3.04 3.01 2.92 3.18
1061.3 1245.6 1671.3 2090.0 2162.5
Jute fibre: linear density 2.02 tex, tenacity 26.6 g/tex, breaking extension 1.04%. Polyester fibre (36 filamemts): linear density 11.5 tex, tenacity 39.3 g/tex, breaking extension 24.0%. Nylon fibre (20 filaments): linear density 9.6 tex, tenacity 37.4 g/tex, breaking extension 45.6%.
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3.0 C B 2.5
2.0 Load (kg)
A 1.5
1.0
0.5
0 0
0.5
1.0 1.5 2.0 Elongation (%)
2.5
3.0
1.23 Load–elongation curves for jute–polyester wrap yarn [21].
through the properties of the elastic core and the tension under which it is incorporated into the yarn.
1.8.7 Plied/cord yarn A plied structure improves many properties such as: ∑ ∑
Ability to absorb processing stress Improvement in cohesion by the entrapment of hairy ends or broken filaments ∑ Balancing of torque liveliness ∑ Improvement in load/stress distribution amongst filaments ∑ Improvement in tensile recovery behaviour. Typical load-elongation behaviour of tyre cord (construction parameters shown in Table 1.15) is shown in Fig. 1.24. It may be observed that either a decrease in the strand twist (keeping the cord twist constant) or a decrease in the cord twist (keeping the strand twist constant) results in steeper curves. The bending rigidity of a ply or cord increases with the ply or cord twist level, as with increase in twist the degree of freedom of fibre movement gets restricted within the structure.
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Table 1.15 Construction of cord yarns Type of cord
Fineness Construction (den)
Cord twist (turns/10 cm)
Kevlar A 9000 1500/2 × 3 20 B 20 C 20 Polyester A 9000 1500/3 × 3 11 B 29
Strand twist (turns/10 cm) 10 20 30 25 25
100 B A 80 B
40 C A
60 Load (kN)
Load (kN)
30
40
20
20
10
0
0
2 4 6 Elongation (%) (a) Kevlar
8
0 0
2
4 6 8 10 12 14 Elongation (%) (b) Polyester
1.24 Load–elongation curves for various kevlar (a) and polyester (b) cords as described in Table 1.15 [23].
1.9
Applications of mono- and multifilaments, tape, core spun, plied and cabled yarns
Application of technical yarns is primarily based upon the properties of their constituent fibres. The intrinsic properties of the raw material, i.e. the fibre, is of fundamental importance in this regard. It may so happen that a few fibres
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may suit a given product specification and one has to choose one of them keeping in mind the cost, availability, manufacturability, etc. Many times the properties that are required in a specific product are such that no single fibre will suit it in all respects and in such cases an optimum combination of different fibre types and their spatial arrangement within the yarn becomes of paramount importance. It may so happen that to arrive at a specification closest to the product, not only fibre but also yarn combinations may need to be considered. Some typical examples of fibres used for a few technical products are shown in Table 1.16. One can find that the use of natural fibres in technical textiles is becoming more limited, though biodegradability is one of the strong attributes of all natural fibres and a renewed interest in the use of natural fibres in composite making can be observed. Many uses of technical yarns have been mentioned by Gong and Chen [24].
1.9.1 Monofilament yarn Monofilaments are suitable for those applications where stiffness is required, such as agrotech (ropes and nets), indutech (filters, conveyors, brushes Table 1.16 Yarn used according to application or special properties Generic products Products
Yarn types according to source or fibre
Protective textiles (mechanical, chemical, electrical)
Parachutes, airbags, Nylon, polyester, viscose electrostatic shielding fabric, rayon, PVA (polyvinyl alcohol) mountaineering ropes, safety nets, conducting textiles
Transport
Seat belts, tyre cords, conveyor belts, car seat covers, nets, hoses, sail cloth, tarpaulins
Acrylic, nylon, wool, polyester, polypropylene, aramid, carbon, polyethylene, glass, etc.
Geotextiles
Soil separators, soil reinforcement, filters
Jute, coir, polypropylene, polyethylene, polyester
Construction
Awnings, tarpaulins, safety nets
Acrylic, nylon, polyethylene, polypropylene
Technical apparel Bullet-proof, fire-retardant and heat-resistants products, gloves, sewing thread, sleeping bags, elastic yarn Farming
Sacks, bags, fishing nets, bird nets, cords, twines
High-modulus polyethylene (dyneema) aramid (kevlar, nomex, Twaron), modacrylic, FR viscose, FR polyester, wool, acrylic Cotton, flax, jute, polypropylene
Medical and hygiene Sutures, support bandages, Cotton, PVA (polyvinyl body bags, towels, mops, alcohol), silk, PTFE surgical gowns, swabs, etc. (polytetrafluoroethylene)
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screen printing cloth), sporttech (racquet string, fishing lines), cloth tech (zip fasteners, sewing thread) and meditech (pressure garments). Ropes and cords used in agriculture and fisheries are made from 0.2–0.5 mm diameter polyethylene and polypropylene fibres. Nylon monofilaments 0.1–5 mm in diameter are used for rope making. Conveyor belt fabric for paper machines requires high chemical and temperature resistance, toughness, durability, abrasion resistance and dimensional stability. Polyester and nylon (flat, square and rectangular) yarns are used to make the fabric to control air permeability and to give support to the paper. Filament diameter is typically 0.15–0.30 mm. Poly(ether ketone) (PEEK) and polyphenylene sulfide (PPS) are used for high-temperature applications. Hollow monofilaments are used to make softer sewing thread. Nylon monofilament 0.1–0.3 mm in diameter is used for sewing thread. HDPE, LDPE and PP monofilament can be used as shrink sleeve in the electrical industry, and as reinforcing cord in hoses. HDPE and LDPE can also be used in sutures and orthopedic braces. Polypropylene and nylon (0.3–0.5 mm diameter) are also used as medical thread. Elastomeric monofilaments can be used to make pressure garments. Nylon and polyethylene monofilaments (0.4 mm diameter) are used in fishing line and netting, in sports racquets and in conveyor belts and safety straps. PVC monofilaments, being cheap, and nylon monofilaments, being more resistant to abrasion, are used for domestic brushes, polypropylene for street cleaning and paint brushes, and polyethylene monofilament for car wash brushes, being soft and flexible. Some products suitable for monofilaments are suggested in Table 1.17.
1.9.2 Multifilament yarn Multifilament yarns have a wide range of uses. In almost all types of technical textile products, multifilament can be used. The fineness of individual filaments in a multifilament yarn lies between 0.22 and 1.67 tex and their diameter could be 1 mm or less. To give two examples, strength, elongation, flexibility, permeability and weight are the most important characteristics of airbag fabric, so the yarn should be strong and flexible, hence low denier per filament multifilament nylon or polyester yarns are used. In the case of car seat belts, shock absorption is the most important criterion. The body has to be decelerated at a specific rate which does not cause injury to the body. Hence, nylon and polyester multifilament yarns are ideal. Some typical examples are shown in Table 1.18.
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Table 1.17 Products from monofilament yarns Product Requirements Fibre used
Filament diameter
Conveyors for Temperature, Polyester, 0.5–0.8 mm paper making dimensional stability, polyphenylene machines abrasion resistance, sulphide (PPS), exposure condition poly(ether ether keytone), nylon Filter fabrics Temperature, exposure Polypropylene, nylon 0.03–0.4 mm (open sieve) condition 6, polyester, PPS, PBTP, PEEK Brushes (floor brush, Recovery, creep Nylon, polyethylene, 0.1–1.5 mm street cleaning, performance, abrasion PVC, polypropylene painting, car wash, resistance, cost, food cleaning, dish temperature resistance washer) Fabrics for screen Shape and regularity Polyester 0.03–0.1 mm printing industry of textile cell, dimensional stability Table 1.18 Products from multifilament yarns Seat belt webbing Requirement : Light weight, high abrasion resistance, excellent recovery characteristics, heat and light resistance, flexibility in use, etc. Fibre used: High tenacity polyester multifilament yarn Linear density or diameter : 500/750/1000/1500 dtex Airbags Requirement : High tear strength, controlled air permeability, foldable Fibre used: High tenacity multifilament nylon 6 and 6.6, polyester Linear density of yarn: 210/420/630/840 den Linear density or diameter of fibre: 2.5–4.2 den Tenacity and elongation: 75–84 cN/tex and 20–22% Sail cloth Requirement : Light weight, sunlight resistance, tear resistance Fibre used: Polyester, polyethylene yarns (Spectra, Dyneema) Linear density : 5–550 dtex Cut resistance fabric Requirement : strong Fibre used: PBO, aramid, polyethylene Linear density : 400–500 den Safety belts Requirement : shock absorption, flexible, abrasion resistance Fibre used: nylon and polyester multifilament yarn Linear density : 550–5500 dtex Tenacity and elongation: 4.9–6.2 cN/dtex, 27% Tyres Requirement : tensile fatigue resistance Fibre used: nylon, polyester multifilament yarn Linear density : 800–1500 den
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1.9.3 Tape yarn Tape yarns are mostly used in woven products (sacks) and special cordage. Being flat they can provide good cover. Polypropylene tapes (20–40 mm wide, 0.06–0.1 mm thick and of fineness 1600–2700 tex are typically used for these applications.
1.9.4 Core spun yarn Core spinning offers enormous scope to combine different fibres by selectively positioning them in the core and the sheath in order to engineer a yarn for a specific end use. Three-ply (polyester core and cotton sheath) yarns are used as sewing threads. Polyester provides the strength whereas cotton provides a frictional surface and protects it from melting at high sewing speed. Yarns with fibreglass or carbon filament in the core and with aramid fibre cover are used in flame-retardant fabric. Yarns with an elastic core and nylon or polyester as sheath are used to produce stretch fabrics, swimsuits, elastic tape, pressure garments, etc.
1.9.5 Plied and cabled yarn Rope yarn Rope yarns are made from both natural and synthetic fibres. Natural fibre yarns such as manila and sisal have a fineness in the range of 560–6700 tex [25]. They are usually Z twisted. The tenacity of such yarns lies in the range of 21–30 g/tex. Rope yarns can be either single or folded. Since twisting causes loss in strength (to the order of 50%) from fibres to yarns, minimum twist is imparted into the yarns. The purpose of twist is more to hold the fibres together for ease of processability. Besides, it also improves abrasion resistance. For synthetic fibres, the common fineness of rope yarn is 3105 tex with twist around 50 turns/m. Eighteen basic yarns of 93 tex (840 den) are combined together to form a single yarn of 1680 tex and then two or three of them are twisted together to form rope yarn. There is no standard for rope yarn diameter and it is usually chosen to be one-tenth of the rope diameter. Tyre cord yarn Tyre cord yarns are of cabled structure and made from nylon, polyester and aramid fibres. Nylon has high strength and excellent fatigue resistance. However, owing to its low glass transition temperature and lower modulus, it is not suited for high-speed application. Polyester fibre yarn, on the other hand, being superior to nylon yarn in these respects, is preferred in radial
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and high-speed tyres. Aramid yarns, although superior in all other respects, find limited use due to their low compressive fatigue resistance. The size and tenacity of typical tyre yarns are 1100 dtex and 6.6 N/dtex for PET, 1400 dtex and 8.4 N/dtex for nylon 6,6, and 1670 dtex and 20.3 N/dtex for kevlar fibres, respectively [26].
1.10
Market
The market for technical yarns is intimately linked to the growth of technical textiles. According to Beckmann [27] the factors responsible for growth are: ∑ Advancement in material and processing technology causing replacement of solid materials used in building and composites ∑ Stringent environment (filtration) and safety regulations (protective clothing) ∑ Growth in income in developing countries leading to more recreational activities (sports) ∑ Ageing population. Technical yarns are dominated by polyester and polyamide which together have captured 85% of the market. The most prosperous markets are in PR China, Taiwan and Brazil. Annual global production has been estimated to be 2.6 million tonnes [28]. The major consumer of industrial yarn is the automotive industry. Keldany [29] has reported that the demand for indutech textile (finest filter to conveyor belt) will increase mainly in China and India. The demand for buildtech textile is directly dependent on construction activity and major international events such as the Olympic Games, World Cup, Asian Games, Commonwealth Games, etc., as many non-permanent structures are erected that need covering fabrics. The growth of geotextiles used in building roads, railways, bridges, dams, etc., will be in the order of 5.6%. The demand for packagetech requiring heavy dense fabrics for sacks, flexible intermediate bulk containers and light lapping fabrics is directly linked to the growth of the economy. Agrotech, consisting of shading fabrics to ground coverings for weed control and growth, is difficult to estimate. Global spandex production is estimated to have been 340,000 tons in 2006 and is estimated to increase to more than 500,000 tons per year in 2010 [30]. The fastest-growing consumer markets are in northeast and southern Asia. The consumption of fibres in technical textiles is still much lower in comparison to their apparel and home textile uses and the market is bound to grow in the future.
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1.11
Technical textile yarns
References
1. Byrne, C. (2000) ‘Technical textile market – an overview’, in Handbook of Technical Textiles ed. A. R. Horrocks and S. C. Anand, The Textile Institute, CRC Press, Woodhead Publishing, Cambridge, UK. 2. Krässig, H.A., Lenz, J and Mark, H.F. (1984) Fiber technology: from Film to Fiber, International Fiber Science and Technology Series 4, Marcel Dekker, New Yok. 3. Uster News Bulletin, No. 37, August 1990, Zellweger Uster. 4. Dang, M., Zhang, Z. and Wang, S. (2006) ‘Properties of wool/spandex core spun yarn produced on modified woolen spinning frame’, Fibres and Polymers 7(4), 420–423. 5. Alagirusamy, R., Fangueiro, R., Ogale, V. and Padaki, N. (2006) ‘Hybrid yarns and textile preforming for thermoplastic composites’, Textile Progress 38(4), 1–71. 6. Brunnschweiler, D. (1953) ‘Braids and braiding’, J. Textile Institute, 44, 666–686. 7. Xue, P., Park, K.H., Tao, X.M., Chen, W. and Cheng, X.Y. (2007) ‘Electrically conductive yarns based on PVA/carbon nanotubes’, Composite Structures 78, 271–277. 8. Shaikhzadeh Najar, S., Kaynak, A. and Foitzik, R.C. (2007) ‘Conductive wool yarns by continuous vapour phase polymerization of pyrrole’, Synthetic Metals 157, 1–4. 9. Fugetsu, B., Akiba, E., Hachiya, M. and Endo, M. (2009) ‘The production of soft, durable and electrically conductive polyester multifilament yarns by dye printing them with carbon nano tubes’, Carbon 47, 527–544. 10. Cheng, K.B. and Ueng, T.H. (2001) ‘Friction core spun yarns for electrical properties of woven fabrics’, Composites, Part A 32, 1491–1496. 11. Hearle, J.W.S., Grossberg, P. and Backer, S. (1969) Structural Mechanics of fibers, yarns and fabrics, Wiley interscience, New York. 12. Porwal, P.K., Beyerlein, I.J. and Phoenix, S.L. (2007) ‘Statistical strength of twisted fibre bundles with load sharing controlled by frictional length scales’, Journal of Mechanics of materials and structures, 2(4), 773–790. 13. Scardino, F. (1989) ‘An introduction to textile structures and their behaviour’, in Textile Structural Composites, ed. by T.-W. Chou and F.K. Ko, Elsevier Science, New York, 1–26. 14. Madsen, B., Hoffmeyer, P., Thomsen, A.B. and Liholt, H. (2007) ‘Hemp yarn reinforced composites–yarn characteristics’, Composites, Part A 38, 2194–2203. 15. Hearle, J.W.S., Hollick, L. and Wilson, D.K. (2000) Yarn Texturing Technology, The Textile Institute, CRC Press, Woodhead Publishing, Cambridge, UK, p. 61. 16. Hearle, J.W.S. (1989) ‘Mechanics of yarns and non-woven fabrics’, in Textile Structural Composites, ed. T.-W. Chou and F.K. Ko, Elsevier Science, New York, 27–64. 17. Treloar, L.R.G. (1956) ‘The geometry of multi-ply yarns’, J. Textile Institute, 47, T348–T367. 18. McIntosh, B.M. (1994) ‘Specialized uses 4: Monofils’, in Synthetic Fibre Materials, ed. H. Broody, Polymer Science and Technology Series, Longman Scientific and Technical, Harlow, UK, 261–272. 19. Morton, W.E. and Hearle, J.W.S. (1993) Physical Properties of Textile Fibres, The Textile Institute, Manchester, UK, 410–412. 20. Fourné, F. (1999) Synthetic Fibres–Machines and Equipment, Manufacture, Properties, Hanser Publishers, Munich, 786.
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21. Sengupta, A.K., Chattopadhyay, R.S., Sengupta, S. and Khatua, D.P. (1991) ‘Some studies on structure and properties of wrapped jute (parafil) yarn’, Indian Journal of Fibre and Textile Research 16, 128–132. 22. Miao, M., How, Y.L. and Cheng, K.P.S. (1994) ‘The role of false twist in wrap spinning’, Textile Research Journal 64(1), 41–48. 23. Chattopadhyay, R. and Kawabat, S. (1993) ‘Geometry of cord cross-section and contraction of cord diameter due to longitudinal extension’, Indian Journal of Fibre and Textile Research 18, 1–7. 24. Gong, R.H. and Chen, X. (2000) ‘Technical yarns’, in Handbook of Technical Textiles ed. A.R. Horrocks and S.C. Anand, The Textile Institute, CRC Press, Woodhead Publishing, Cambridge, UK, 42–60. 25. Klust, G. (1983) Fibre Ropes for Fishing Gear, Food and Agriculture Organization of the United Nations, Farnham, Surrey, UK, 12–28. 26. Chawla, S.K. (1994) ‘Rubber composites’, in Synthetic Fibre Materials, ed. H. Brody, Longman Scientific and Technical, Harlow, UK, 202–230. 27. Beckmann, R. (2000) ‘The international market for technical textiles from the market standpoint’, Melliand International 6, 136. 28. Anon. (2007) ‘Global market trends for industrial yarns’, Melliand International 3, 168. 29. Keldany, R. (2005) ‘Market trends for technical fabrics’, Melliand International 4, 308–309. 30. Anon. (2007) ‘Global elastane (spandex) yarn production 340,000 tons’, Melliand International 3, 166.
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2
Advances in yarn spinning and texturising
R. V. M. G o w d a, V.S.B. Engineering College, India
Abstract: This chapter deals with the advances in yarn spinning technologies, developments in yarn properties and specific applications of various yarns. It also discusses the prominent yarn texturising technologies, innovations and technical applications of texturised yarns. Finally, it highlights the future trends in yarn spinning technologies. Key words: advances, yarn spinning technologies, yarn properties, yarn texturising.
2.1
Introduction to various yarn spinning technologies
Ring spinning, invented by John Thorpe in 1830, has been very successful in producing yarns from staple fibres. It has been reported in the literature that up until the 1960s most of the yarns produced from staple fibres were spun on the ring spinning system, which enjoyed a monopolistic status of production. Though ring spinning is a versatile system for processing a wide variety of fibres into a broad range of counts, spinners, researchers and machine manufacturers have become increasingly aware of its technological and economic limitations, which were the subject of much discussion, and as a result, machine makers and researchers have been on the lookout for new and future oriented spinning technologies. The aim of most of these new technologies was to increase productivity, improve or at least retain yarn quality, and ensure increased efficiency in subsequent processing. It was in 1967 that the aim became a commercial possibility with the introduction of the BD 200 rotor spinner, which did away with the concept of spindle twisting. Since then, the rotor spinning system has established itself in the coarse and medium count range. However, as rotor speeds reached 175,000 rpm, the rotor diameter had to be decreased to around 28 mm to accommodate such a high speed. Therefore, it was felt that this system too had reached its practical limits with regard to productivity. Thus the search for other spinning systems continued. In 1973, Ernst Fehrer developed the friction spinning system, which was commercialised in 1977 under the name DREF 2. In this system, the spinning speed is as high as 300 m/min and is not limited by the yarn tension. Theoretically, very high rotation speeds are attainable. At the beginning 56 © Woodhead Publishing Limited, 2010
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of the 1980s, Murata Jet Spinning was developed and commercialised by Murata Machinery, Japan. Today, this system is commercially successful in the production of medium and fine counts from synthetic fibres, cotton and blends thereof. Murata Vortex Spinning, introduced at ITMA ’99, is another revolutionary system for the production of fasciated yarns, and is gaining greater momentum in the production of yarns from synthetics and cotton in pure form or blends. Of late, other spinning methods such as core yarn spinning and wrap spinning have also become popular to produce yarns for certain applications. This chapter discusses the developments in yarn spinning technologies, properties and applications of these yarns.
2.2
Compact spinning
Although ring-spun yarns have unique structure and good strength, they are not perfectly ideal. A careful examination of a ring-spun yarn under a microscope reveals that the integration of many fibres is poor; and such fibres form hairs, which do not contribute to yarn strength [1]. This is due to the effect of spinning geometry during yarn formation. In conventional ring spinning the fibres supplied by the drafting system are collected by the spinning triangle and integrated into the yarn structure. For a specific yarn of given count and elongation values, the width b of the spinning triangle depends mainly on spinning tension p; and experiments have shown that b varies inversely with p, but the width B of the fibres fed is always greater than the width b of the spinning triangle (Fig. 2.1). Therefore, the spinning triangle is unable to capture all fibres fed in, which means that the peripheral fibres are either lost or integrated improperly [1, 2]. In view of these shortcomings of the yarn formation process, machine manufacturers thought of exploring possible ways of condensing the drafted ribbon before it is twisted into a yarn. This led to the development of compact spinning. The prominent compact spinning methods are the ComforSpin process of Rieter, EliTe spinning developed by Suessen, the Air-Com-Tex process of Zinser and the RoCoS compact spinning system of Rotorcraft. B
B
b
b Bring = Bcom4 bring > bcom4
Ring spinning
ComforSpin®
2.1 Yarn formation in ring spinning and Comfor spinning [3].
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The principles of working of these methods of condensing the drafted strand of fibres are described below.
2.2.1 ComforSpin process In Rieter’s ComforSpin process, an intermediate zone is inserted between the draft and yarn formation zones. In this zone, the ready-drafted ribbon of fibres is condensed laterally by means of aerodynamic forces. A perforated drum replaces the delivery roller of the drafting system (Fig. 2.2). A fixed suction system generating a vacuum is fitted inside this perforated drum, which results in a current of air flowing from outside into the drum. The fibres supplied from the delivery nip line of the drafted system are then held firmly on the surface of the perforated drum and move with the circumferential speed of the drum. A subsequent top roller and the drum clamp the spinning triangle, i.e., the yarn formation occurs immediately after this second nip. The web of fibres is condensed in the intermediate zone between the two top rollers on the perforated drum, as a result of which the width B of fibres fed is
1 Perforated drum 4
2 Suction system
3
3 Bottom roller 4 Top roller 2
5 Nip roller 6 Air guide element
5
6
1
Air guide element Air
Air
Suction
2.2 ComforSpin process [3].
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approximately equal to that of the spinning triangle. The compacting effect depends largely on the combination of the metal cylinder with precision perforation, suitable surface structure, flexible suction inserts, and air guide elements. The cross-section of the compacting system in the illustration given in Fig. 2.2 indicates the way the air is guided to the fibre strand for a full compacting effect [3]. The condensed yarn so produced, known as COM4 yarn, as compared to an equivalent conventional ring yarn, exhibits less hairiness, higher strength and elongation, less environmental impact and unequalled wearing comfort [3]. The term COM stands for ‘comfort’, which has always been a reflection of lifestyle and the greatest feeling of well-being, and the number 4 denoted the four distinct advantages of COM4 yarn as highlighted above. The improvement in COM4 yarn quality can be indicated by the COM4 value, which is given by [1]:
COM4 value =
100,000 yarn twist (tpm) ¥ Yarn hairiness, H
2.2.2 EliTe spinning In the EliTe spinning system, developed by Suessen, the drafted ribbon of fibres is condensed with the help of a specially developed lattice apron [4]. A tubular profile subjected to negative pressure is closely embraced by a lattice apron. The delivery top roller, fitted with rubber caps, presses the lattice apron against the hollow profile and drives the apron, at the same time forming the delivery nipping line (Fig. 2.3). The tubular profile has a small slot, which commences at the immediate vicinity of the front roller nipping line and ends in the region of the delivery nipping line. This creates an air
Lattice apron
2.3 Schematic of EliTe spinning [4].
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current through the lattice apron as the slot is located towards the inside of the profile tube. The air current seizes the fibres after they leave the front roller nipping line and condenses the fibre strand, which is conveyed by the lattice apron over a curved path and transported to the delivery nipping line. The suction air pressure and number of holes in the lattice apron influence the condensing action of the fibres. The condensed yarn produced is claimed to have higher strength and lower hairiness as compared to the conventional ring spun yarn.
2.2.3 Air-Com-Tex 700 process With the Air-Com-Tex 700 process [1], offered by Zinser, the drafted strand of fibres emerging from the three-cylinder drafting system is taken from the nip line by the airflow and is condensed under suction on a perforated surface (Fig. 2.4).
2.2.4 RoCoS compact spinning The RoCoS compact spinning system, developed by Hans Stahlecker of Rotorcraft Maschinenfabrik, Switzerland, is incorporated into LMW’s LR6AX short-staple ring-spinning frame. It was exhibited at ITMA 2003 and ITME 2004 [5]. This magnetic compacting system replaces the normal top front roller with a pair of smaller rollers between which is a condenser. The condenser is held against the bottom front drafting roller by means of a magnet (Fig. 2.5(a)). The RoCoS device (Fig. 2.5(b)) consists of the cylinder (1 in Fig. 2.5(a)), the front roller (2), the delivery roller (3), the Supra-Magnets equipped with ceramic compactors (4), the supporting bridge, the yarn guides and the top roller holders with the weighting spring [6]. RoCoS, the Rotorcraft Compact Spinning System, works without air suction and uses magnetic mechanical principles only. The bottom roller (1) supports the front roller (2) and delivery roller (3). The condensing zone extends from clamping line A
2.4 Air-Com-Tex 700 process [1].
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A
4 2
B
4 3
1 (a)
(b)
2.5 (a) Schematic of RoCoS compact spinning; (b) RoCoS device [6].
to clamping line B. The very precise magnetic compactor (4) is pressed by permanent magnets without clearance against cylinder 1. It forms together with the bottom roller an overall enclosed compression chamber whose bottom contour, the generated surface of cylinder 1, moves synchronously with the strand of fibres and transports this safely through the compactor. In respect of yarn fineness and yarn twist, the standards usual in the industry are applicable. Compactors for coarse, medium and fine count yarns ensure ideal compacting. According to Stahlecker, RoCoS 1 is suitable for cotton, both pure and as blends with synthetic fibres, as well as for pure synthetics with a maximum staple length of 60 mm (2.5 inches). On the other hand, RoCoS 2 is suitable for wool, both pure and as blends with synthetic fibres as well as for pure synthetics, having a minimum staple length of 50 mm (2 inches). The compact-spun yarns, in addition to their extensive applications in apparel production, find scope for production of technical yarns such as sewing threads, embroidery threads, core-spun yarns, etc.
2.3
Rotor spinning
2.3.1 Principle of operation Rotor spinning, working on the principle of open-end spinning, consists of the following operations in sequence [7]: 1. 2. 3. 4.
Opening of feed sliver into individual fibres Assembling of individualised fibres Twist insertion Withdrawal of resultant yarn and winding onto a package.
In rotor spinning, the individualised fibres carried by the air current are deposited continuously on the internal peripheral surface of a rapidly rotating drum, called the rotor, to form a fibrous ring (Fig. 2.6). The rotation of the
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3
1
4
2
1. Feed sliver 2. Feed roller 3. Opening roller 4. Transport tube
5. 6. 7. 8.
6
6
5 Rotor groove Withdrawal tube Delivery rollers Yarn arm inside the rotor
2.6 Principle of rotor spinning [7, 8].
rotor imparts twist to the fibrous ring, which is then peeled off and withdrawn along the axis of the rotor. The first rotor spinning machine, the KS 200, was demonstrated publicly at Brno in 1965, and the first commercial machine, the BD 200, appeared in 1967. Since then, rotor spinning has evolved through several stages and is now very well established in the coarse and medium count sector. The sequence of operations involved in rotor spinning can be broadly grouped into four units, namely fibre individualisation, fibre assembly, twist insertion, and withdrawal of resultant yarn. All these operations are described briefly as below [7, 8]. Fibre individualisation A drawn sliver, generally a two-passage drawframe sliver, is fed by a feed roller at a certain rate to an opening roller. The opening roller, or combing roller, clothed with saw teeth or pinned teeth and rotating at high speed, opens the sliver into individual fibres. The opening roller speed may vary from 6500 rpm to 9000 rpm, depending upon the type, length and fineness of fibre, and the thickness of feed. The profile of the opening roller teeth also varies with the type of fibre to be processed. Fibre assembly The individual fibres are carried forward from the opening roller by an air current through the feed tube or transport tube, the conical shape of
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which accelerates the air current, leading to improved fibre orientation and straightness. The fibres carried by the air current are deposited at the groove of the rotor in the form of a ring. Twist insertion As the rotor rotates, the centrifugal force presses the fibre band against the inner peripheral surface of the rotor, causing it to rotate and thereby inserting twist to the fibre assembly. The rotational speed of the rotor may vary from 50,000 rpm to 175,000 rpm, depending upon the fibre type and yarn count to be spun. Withdrawal of resultant yarn The spinning of yarn starts by inserting a seed yarn through the withdrawal tube. The yarn end makes contact with the rotating tail of the fibre assembly. The yarn so formed is withdrawn continuously at certain rate (100–250 m/ min) by take-up rollers and wound onto a package.
2.3.2 Latest developments in rotor spinning Rotor spinning has become very well established in the coarse and medium count sector. Due to increasing demand on productivity, rotor speeds have been reaching as high as 175,000 rpm with the rotor diameter correspondingly decreasing to 28 mm. Following are some of the highlights of the latest developments in rotor spinning machinery and processing. To improve the yarn quality further, Suessen has modernised the SE 8 and SE 9 spin boxes into compact spin boxes SC 1-M and SC 2-M on their Autocoro 288 rotor spinner [9] with the incorporation of the following special functional elements/accessory devices. Adjustable BYPASS The adjustable BYPASS, which is an auxiliary opening for air, allows a higher air velocity in the fibre feed chamber and a lower air velocity in the trash extraction chute, which improves fibre removal from the opening roller, reduces dolphin jumps, i.e., less dirt in the yarn, facilitates a turbulence free airstream in the trash extraction chute, reduces extraction of good fibres, i.e., makes better usage of fibres, permits accurate setting of the extracted trash percentage, keeps the rotor groove clean over a longer period, reduces end down and imperfections, makes clearer cuts, and improves yarn quality and spinning stability.
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Speedpass The SPEEDPASS increases the air velocity from the opening roller housing through the fibre channel up to the rotor, and thus ensures better removal of synthetic fibres, in particular polyester, which has a lapping and recirculating tendency. An additional cavity, the ‘swan neck’, in the opening roller housing is provided to improve sliding of fibres into the fibre channel. Also, the newly designed opening roller type S 43 DN with special coating improves fibre removal. Torque-Stop The Torque-Stop is a small, easily replaceable twist-blocking device, which increases false twist in the yarn arm inside the rotor. The Torque-Stop is generally situated inside the navel and either serves to reduce the number of end breaks for a given twist factor or permits a reduction in the twist factor for a given number of end breaks. In any case this device will ensure a substantial increase in productivity. Corolab ABS This system is used to detect coloured foreign particles on the yarn exterior in the Autocoro rotor spinning machine. With this system, the measuring head is located in the yarn take-off tube in the spinning box directly behind the Torque-Stop. The detection system is based on the absorption principle. The measuring head consists of a light impermeable circle in which four illuminating diodes are located as transmitters and four photo diodes as receivers. As yarn with no foreign fibre absorbs less light than one contaminated by foreign fibres, the quantity of absorbed light varies and the foreign fibre is detected. The length, colour intensity and number of foreign fibres can be determined and the yarn portion containing foreign matter is cleared. Table 2.1 depicts the improvement in yarn quality and the increase in production caused by modernisation of the spin boxes in rotor spinning [9,10]. Autocoro 360 is the new rotor spinning machine introduced very recently by Schlafhorst that yields greater productivity and flexibility with four Coromats per machine. It has up to 360 spinning units and take-up speeds of up to 300 m/min are possible [11]. The innovations in important functional parts of this machine are highlighted below. Corobox SE 12 spinbox The universal Corobox SE 12 spinbox is accurate and more economical and offers greater flexibility with the intelligent Single Drive Sliver Intake
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Table 2.1 Benefits of SC 1-M and SC 2-M spinboxes [7, 9] Description 20 Ne cotton 30 Ne cotton
SE 8
SC 1-M
SE 8
SC 1-M
Rotor speed (rpm) 67,000 84,000 85,000 117,000 Delivery rate (m/min) 155 185 83 115 Unevenness (CV%) 12.3 12.2 15.2 15.0 IPI 8 5 67 65 Tenacity (cN/tex) 12.0 12.8 10.6 12.5 Production increase – +25.3% – +38%
20 Ne PES/cotton (50:50) SE 8
SC 2-M
95,000 150 14.8 82 13.0 –
96,000 168 13.5 65 13.9 +12%
(SDSI) and 20- to 450-fold drafts. No matter whether the yarns spun are from natural or artificial fibres or blends of these, or are smooth or structured yarns, the Corobox SE 12 is capable of handling all applications. This new spinbox gives the Autocoro 360 a level of flexibility and a yarn quality never previously achieved. The SDSI guarantees a precisely defined fibre feed by means of stepping motors in each spinbox. This is crucial for the manufacture of reproducible fancy yarns. With the Corobox SE 12, only one feed is required for all yarn counts, a major advantage. Even coarse slivers of up to 7 ktex are spun into fine yarns due to the wide draft range of 20- to 450-fold [11]. Fancynation This is a new route to fancy yarn production with a unique drive and control concept that results in higher productivity. Fancynation is the modular hardware and software integrated into the Autocoro 360 to facilitate the production of fancy yarns. Fancy yarn manufacture is more productive and reproducible than ever before with fancynation, as the mechanical constraints commonly encountered in the past have been eliminated by the Corobox SE 12 with SDSI. The central platform for all effects is the FancyPilot. A variety of tools such as the QuickDesigner, 2D-interactive GraphicDesigner and 3D simulations are used to generate and modify effects easily, quickly and with little effort on the screen. Repeat changes, the simulation of effects on yarn panels and in knits and wovens on the screen make product development easier. Machine setting parameters are linked automatically to effect data in the software and setting recommendations are stored with spinning components, also enhancing the reproducibility of fancy yarn production. Other notable system modules are FancyControl for monitoring the quality of the yarn spun online, FancyProfile for displaying the yarn diameter and progression of effects, FancyOasis Gold with extended simulation functions such as stonewash finishes, and FancyLink for measuring and entering yarn patterns.
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Other fundamental elements of fancy yarn production on the Autocoro 360 include new spinning components developed specially for fancy yarns, such as GT rotors and a compact feed tray, along with the precise, electronically controlled spinning vacuum achieved with the Electronic Vacuum Adjustment (EVA) system. Coropack The Autocoro packages have set new standards with the following parameters: ∑ ∑
Coro Value Package (CVP): compact, optimum unwinding properties Heavy Weight Package (HWP): economical, up to 5 kg weight.
The new CoroPack generation of packages is synonymous with greater efficiency and quality. The Coro Value Package (CVP) guarantees a low, homogeneous winding tension that will not have a detrimental effect on the yarn. The yarn elongation is thus up to 1% higher than on conventional packages. As a result, the new packages are distinguished in weaving and knitting mills by up to 70% fewer yarn breaks [11]. Polypropylene clearing system The Autocoro 360 is equipped with the new Corolab 8 and Corolab 8PP yarn monitoring system on which even foreign fibres of materials such as polypropylene or nylon used in bale packaging can be cleared along with film residues. The Corolab 8PP is based on the tribo-electric effect. Polypropylene fibres trigger a clearer intervention, in the case of both cotton yarns and blended cotton yarns. Every basic clearer in the Corolab 8 system is already configured in readiness for retrofitting the polypropylene sensor, so that this can be installed at any time subsequently [11]. Magnetic rotor positioning system (MRPS) This system is an optional arrangement provided on the Autocoro 360 rotor spinner, where the new rotor axial bearing assembly of the Corobox SE 12 fixes the rotor entirely without contact. The following are the salient features of this system [11]: ∑ Energy saving and oil-free or lubricant-free drive system ∑ Clean spinbox environment ∑ Long cleaning and extended maintenance intervals ∑ Carbon fibre reinforced rotor brake ∑ Reduced spare parts requirements.
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Rieter Machinery also came out with their innovative R 40 rotor spinner [12], which is readily commercialised. These latest machines have salient features such as rotor diameters from 28 to 56 mm, rotor speeds up to 140,000 rpm, delivery speeds up to 220 m per minute, overall draft up to 400, VARIOdraft – infinitely variable and adjustable draft, twist, and winding tension, ROBOfeed – automatic sliver insertion system, SERVOcan – automatic can handling and changing process, SERVOcone – automatic package linking and removal system, and connection to the SPIDERweb mill data system. All these innovations have led to increased rotor speeds up to 170,000 rpm, reduced ends down per kg yarn by up to 70%, thus increasing machine efficiency and production, enhanced yarn evenness and reduced yarn imperfections and classimat faults by up to 40%, reduced variation in yarn patterns from spinning position to spinning position, lengthened cleaning and maintenance intervals by up to 30%, and produced cleaner yarns. As regards the production of technical yarns, rotor spinning offers scope to produce core-spun yarns, cable and tyre-cord yarns, etc.
2.4
Friction spinning
2.4.1 Principle of operation Friction spinning is an ‘open-end’ and/or a ‘core–sheath type’ spinning, in which the yarn formation takes place with the aid of frictional forces in the spinning zone. Friction spinning, as originated earlier, was based on the principle of ‘open-end spinning’, and later on ‘core–sheath’ type spinning. The different machine versions of friction spinning developed over the years include the Masterspinner from Platt Holingsworth and a series of DREF spinning machines from Fehrer AG. The Masterspinner was a laboratory model that spins staple fibres into yarns in the count range of 10–40 s Ne at delivery speeds up to 300 m/min. This machine, however, could not attain much commercial success [7]. Fehrer developed the DREF friction spinning system in 1973. In the very first machine, the DREF 1 friction spinner, due to the absence of positive control over the assembly of fibres, a lot of slippage occurred between the fibre assembly and the perforated roller, which reduced the twisting efficiency. Hence this development could not be commercialised. In order to reduce slippage and improve twisting efficiency, the concept of enclosing the fibre assembly between two perforated friction drums was introduced. This formed the basis for the commercial development of later DREF spinning machines, namely DREF 2, DREF 3, DREF 2000 and DREF 3000. The DREF 2 friction spinner operates on the basis of a patented mechanical/ aerodynamic spinning system and is typified by the use of two perforated
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friction drums with internal suction and the same direction of rotation. A schematic drawing of the DREF 2 friction spinner is shown in Fig. 2.7 [13]. It essentially consists of a specially designed inlet system, which retains the slivers and provides the required draft. These drafted slivers are opened into individual fibres by a rotating carding drum (opening roller) covered with sawtooth-type wire clothing. The individualised fibres are stripped from the carding drum by a centrifugal force supported by an airstream from the blower, and are transported into the nip of two perforated friction drums where they are held by suction. The fibres are subsequently twisted by mechanical friction on the surfaces of the drums. The suction through the perforations of the drums assists this process besides helping in the removal of dust and dirt, thereby contributing to the production of a cleaner yarn [14]. In 1977, the first DREF 2 machine appeared in the market, which was the first friction spinning machine in practical operation. The low yarn strength and the requirement of a greater number of fibres in the yarn cross-section have restricted the DREF 2 spinning to coarser counts (0.5–6 s Ne). In summer 1978, based on the experiences gained for few years with the DREF 2 spinning machine, the first developmental step for the DREF 3 had taken place and the first machine was introduced into the market by the end of 1981 and beginning of 1982. The DREF 3 machine was developed basically to improve the yarn quality, to extend the yarn count to finer ends (up to 18 s Ne) and to produce multi-component yarns. Unlike the DREF 2 and Masterspinner, the DREF 3 is not an open-end spinning machine, but a core–sheath type friction spinning arrangement [15] as shown in Fig. 2.8 [16]. On this machine, an attempt is made to improve Blower air Carding drums Inlet rollers
Suction inserts Spinning drums
2.7 Schematic diagram of DREF 2 friction spinner [13].
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Sheath slivers Winding aggregate Drafting unit II
Outlet Core sliver
Drafting unit I
Spinning aggregate Core feeding
2.8 DREF 3 friction spinner [13].
the quality of yarn, by laying a part of the fibres in an aligned fashion along the direction of the yarn axis in the core. The remaining fibres are wrapped round the core fibres to form the sheath. The sheath fibres are attached to the core fibres by the false twist generated by the rotating action of the drums. Two drafting units are therefore used in this system, one for the core fibres and the other for the sheath fibres. This system produces a variety of core–sheath type structures and multi-component yarns, through selective combination and placement of different materials in core and sheath, in the count range of 1–18 s Ne with a delivery speed as high as 300 m/min.
2.4.2 Latest developments in friction spinning DREF 2000 The DREF 2000 friction spinning machine as shown in Fig. 2.9 [16] is the latest development in friction spinning and attracted the attention of technical textile producers during ITMA ’99. The DREF 2000 employs the classic DREF system with a rotating carding drum opening the slivers into single fibres and a specially designed inlet system being used for sliver retention. The fibres are stripped from the carding drum by centrifugal force and carried into the nip of the two perforated spinning drums. The fibres are subsequently twisted by mechanical friction on the surface of the drums, which rotate in the same direction. The process is assisted by air suction through the drum
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Technical textile yarns Winding aggregate Card slivers
Carding drum Outlet Spinning aggregate Dust extraction Core feed
2.9 DREF 2000 friction spinner [16].
perforations. The machine can produce S-twisted or Z-twisted yarn, without any mechanical alteration. Yarns of 14.5 s Ne can be produced at production speeds of 250 m/min [17]. DREF 3000 The DREF 3000 friction spinning machine exhibited at ITMA 2003 is the latest model in the series of DREF friction spinning machines. It is designed to produce high-tenacity yarns for flame-resistant protective apparel, upholstery, fibre composites, filters and other technical fabrics. The machine achieves production speeds of up to 250 m/min, as well as reduced costs for yarn preparation and maintenance. The touch-screen operation facilitates handling of production parameters and yarn parameters such as yarn count calculation as well as measurement of length and weight, PLC control and links to other computers. In addition, development continues using the DREF 3000 to produce elastomeric-core yarns [16]. Friction-spun yarns find extensive applications in technical textiles.
2.5
Air-jet spinning
2.5.1 Principle of operation Air-jet spinning works on the principle of false twisting/wrapping that produces so-called ‘fasciated yarns’. Air-jet spun yarn consists of a core of parallel fibres wrapped by surface fibres or binding fibres. These yarns are known as fasciated yarns due to the fact that the wrappers are not continuous [7]. Murata Machinery, Japan, exhibited their first Murata Jet Spinner, the MJS 801, at ATME-international in 1982. The Murata Jet Spinner consists of three zones, namely the drafting zone, the yarn formation zone and the
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yarn take-up zone. A drawn sliver is drafted by a four-roller double-apron drafting system (Fig. 2.10). The drafted ribbon of fibres is subjected to the action of an air-jet in two nozzles, which rotates at a very high rate (about 2 to 3 million rpm). The pressure (intensity) of the air-jet in the first nozzle N1 is lower than that in the second nozzle N2. The air-jet in nozzle N1, therefore, cannot influence the core fibres but can readily grasp the edge fibres projecting from the drafted strand at one end and cause them to be wrapped over the core with only a few turns in the direction opposite to the twist in the core [8, 18]. After emerging from nozzle N2 (the main nozzle, which imparts false twist to the core), the core gets untwisted to become a parallel bundle while the edge fibres are wrapped more intensively over the core. The yarn so formed is withdrawn and wound onto a package. The advantage of Murata jet spinning over the Rotofil process and Toray air-jet spinning is that it uses two air-jets while the latter two processes use a single air-jet. With a single air-jet, the free edge fibres are not wrapped as effectively as with two air-jets. In the MJS system, the use of nozzle N 1 with an air-jet of relatively lower pressure – in addition to the main false twist nozzle N2 – ensures grasping of the edge fibres, which are wrapped with a few turns over the core in a direction opposite to the direction of twist in the core. The false twisted core, while getting untwisted, causes the sheath to get wrapped over it with increased intensity and tightness of wrapping. Due to this effective wrapping, the edge fibres hold the core firmly and contribute substantially to the yarn strength. At present, Murata jet spinning is the most commercially successful air-jet spinning system [18].
Air-jet nozzle N1
Air-jet nozzle N2
2.10 Principle of Murata jet spinner [7].
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2.5.2 Latest developments in air-jet spinning Murata Twin Spinner, MTS 881 Murata has developed the Twin Spinner with the objective of producing two folded yarns through a short-cut process. In this machine, the width of cots and bottom rollers are increased to accommodate drafting of two slivers simultaneously, without touching each other. The sliver guides are provided in drafting zones to avoid intermingling of the two strands during drafting [18]. The drafted strands are passed through air-jets separately and are given false twist. Finally, the two strands are brought together and wound in parallel onto a single package, which will be used as a precursor package for a two-for-one twister to produce folded yarn. The operation of the Twin Spinner is controlled by ‘Super Spectron’ and ‘IA-3’. When cyclic yarn unevenness exceeds the control standard, the cause is indicated together with the spindle number in trouble. The packages are wound evenly to a desired yarn length (within ±1%) by ‘Yardage Controller’ [19]. With the innovative idea of the MTS system, the winding process can be eliminated, which results in significant saving on floor space and cost, and an astonishing 10 to 20 times increase in productivity as compared to ring spinning. As compared to MJS yarn, the MTS yarn is less stiffer and fabrics made from the latter are relatively softer. Roller jet spinner The Roller Jet Spinning (RJS) system, first exhibited by Murata at ITMA ’95, is a development of the air-jet spinning concept, with the second air-jet nozzle replaced by a pair of ‘balloon rollers’. The system consists of one air-jet nozzle and a pair of balloon rollers. The air vortex inside the nozzle rotates in a direction opposite to the twisting action of the balloon rollers [20]. The Roller Jet Spinner RJS 804 was demonstrated at ITMA ’99. This system is yet to receive commercial acceptance and popularity.
2.6
Vortex spinning
Murata Machinery has developed a new spinning process called ‘Murata Vortex Spinning’, which is different from air-jet (false twist) spinning.
2.6.1 Principle of operation Vortex spinning takes drawn cotton sliver and drafts it to the desired yarn count (fineness) via a four-roller apron drafting system. The drafted fibres are then sucked into a nozzle where a high-speed ‘air vortex’ swirls the fibres around the outside of a hollow stationary spindle (Fig. 2.11). A rotating air
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vortex twists the free fibre ends around the bridge fibres with true twist [21], producing a ring yarn type of structure. This makes it possible to process carded yarns also. The twist is inserted as the fibres swirl around the apex of the spindle before being pulled down a shaft that runs through the middle of the spindle. The productivity of the MVS system comes through its delivery speed and the fact that it spins yarn directly from sliver, rather than roving. The resultant yarn is cleared and wound directly onto a package that can be sold readily by the mill. Vortex spinning with the MVS 851 machine introduced by Murata at the 1997 Osaka International Textile Machinery Show has been impressively demonstrated with regard to its economic potential through spinning a 15tex yarn from 100% cotton at 400 m/min [21]. Murata exhibited its latest model, MVS 861, at ITMA 2003. The characteristics of MVS yarns and fabrics are observed to be comparable to those of ring-spun yarns, i.e., the fabric made from MVS yarn is reported to be as smooth and as soft as that produced from ring-spun yarn. However, MVS requires reasonably good fibre characteristics to achieve these outputs. Fibres must be clean and strong, have a staple length of at least 28 mm and be uniform in length. The production speed is almost independent of yarn count and is in the range of 300–400 m/min. This process is concurrent with rotor spinning and ring spinning in the count range of 12–40 s Ne. Thus with this system, Murata demonstrates a serious alternative to rotor spinning for medium and long staple cotton spinning. The production cost for 40 s Ne vortex yarn, as
Sliver
Vortex air
Spindle
MVS yarn
2.11 Principle of vortex spinning [22].
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compared to equivalent ring and rotor yarns, is approximately 50% and 60%, respectively. The fully automatic process eliminates all rotating mechanical twist-insertion elements. The flexibility of this technology is significantly higher than that of false twist spinning, and will probably take on the latter. Blended yarns can also be produced without any difficulty. MVS has been hailed as a revolutionary new technology for fasciated yarn production. It appears to have a profound scope for spinning of cotton yarns.
2.6.2 Comparison of MVS with MJS The conventional Murata Jet Spinning (MJS) employs two jets, one of which false-twists the core while the other readily grasps the edge fibres and wraps them in a direction opposite to the direction of twist of the core. The air-jets act on the edge fibres from both sides. The resultant yarn consists of core of twistless and parallel fibres wrapped by the sheath fibres. Murata Vortex Spinning (MVS) with a single jet creates an air-vortex all around, which swirls and twists the free fibres about the bridging fibres, forming a yarn similar to a ring-yarn structure. In air-jet spinning, edge fibres ultimately produce wrapper fibres, and the number of edge fibres depends on the fibres at the outside. On the other hand, in vortex spinning, the fibre separation from the bundle occurs everywhere in the entire outer periphery of the bundle (Fig. 2.12). This results in a higher number of wrapper fibres in the yarn. Both MJS and MVS offer scope to produce core-spun yarns, which find their suitability for production of technical textiles.
2.7
Core yarn spinning
Core yarn spinning is a process for production of core spun yarns. The core spun yarn consists of a central core made up of a filament or an elastane or a bundle of staple fibres covered or wrapped totally by a sheath of staple fibres. The core, which is generally of a strong synthetic filament/fibre,
MJS MVS
2.12 Principle of working of MJS and MVS [23].
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provides desired strength, extension and regularity to the yarn. However, if an elastane is used as core, it provides the desired stretch to the resultant yarn and the fabric. The staple sheath, on the other hand, gives the yarn a spun yarn look, besides acting as a substrate for the application of special chemical finishes. Therefore, core spun yarns are unique in structure and specific to end-use requirements. Core spun yarns can be produced by any one of the methods already described, such as ring spinning, rotor spinning, friction spinning, and air-jet/vortex spinning.
2.7.1 Production of core spun yarns in ring spinning The core yarn can be spun on a conventional ring spinning machine through suitable modification to incorporate a special device for continuous feeding and positioning of the core component. The incomplete core coverage and unsatisfactory strip resistance of these yarns limit their potential end uses. Sawhney et al. [24] have developed an improved method for producing core spun yarns, which is based on a ‘wrap-core-wrap sandwich’ approach, under the name ARS core-spinning system. Figure 2.13 shows a schematic diagram of this new filament-core spinning system. The ringframe is retrofitted with a core stabiliser bar (positioned immediately in front of the front drafting rollers), which has a special groove for the filament-core and a polished surface for the staple wrapper fibres. The two conventionally prepared rovings are kept separated in the drafting zone by roving guides and condensers. Depending on the length of the sheath fibre Cotton rovings
Continuous filament Tension discs Roving condenser Roving spacer Drafting rollers Filament guide Core/wrap spinning system
Spinning ring
Core–sheath yarn 2.13 ARS filament-core spinning system [24].
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being processed, the spacing between the rovings in the drafting zone may vary from 5 to 10 mm. The filament, under relatively high tension, is fed between the two strands of staple fibres behind the nip of the front drafting rollers such that it is not subjected to any drafting action. As the core along with the fibres emerges from the front roller nip, it is guided into the groove in the core stabiliser bar, where the fibre assembly and yarn formation take place. The twisting action produced in the core by the rotating spindle spins the drafted staple fibres onto the filament-core. The core stabiliser bar with an attached twist control guide prevents the flow of twist to the front roller nip, thereby preventing plying (or barber-poling) of different strands that happens in conventional core spinning process. The spacing between the yarn formation point (on the stabiliser bar) and the front roller nip has to be adjusted in relation to the mean fibre length so that individual fibres migrate independently and spin around the core, leading to greater interlocking between the fibres and the core that results in improved strip resistance. The ARS core-spinning system can be used to produce staple core spun yarns also. The roving for the core component is placed between the two rovings that constitute the covering. All the three rovings are separated in the drafting zone using the roving condenser and spacers. As the drafted strands emerge from the front roller nip, they are drawn through a specially designed gripper device. The device has two flat spiral springs (Fig. 2.14) that guide the fibre strands and act as a gripper for the core strand. One spring has a left-hand spiral and the other a right-hand spiral; the two springs face and touch each other. The tension of one or both of the spiral springs can be adjusted to permit a smooth downward flow of the composite material, but without allowing the yarn twist to migrate above the grip of the two springs, resulting in the production of truly coaxial, strip-resistant and almost totally covered core spun yarn. Sawhney and Ruppenicker [25] have produced core spun yarns on the patented ARS core-spinning system using 100% cotton, fibreglass core, and Dyneema core covered with cotton. The yarns were used to develop special-purpose fabrics, such as flame-retardant fabrics for US army tents, fabrics for fire barriers, fabrics for industrial abrasives and sandpapers, etc. The details of the yarns and fabrics are given in Table 2.2.
2.7.2 Production of core spun yarns in rotor spinning The Rieter company offers an innovative process for the production of rotorspun core yarn known as Rotona®. The elastic and non-elastic rotor-spun core yarns can be produced with the BT 904 rotor spinning machine. It has been reported that the Rotona process for manufacturing rotor-spun core yarns is based on a 30-year-old idea. It has been taken up again by Rieter
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Wrap-fibre (1 or 2 rovings) Roving condenser Roving spacer Drafting rollers
Spinning grippers Bracket
Spinning ring Core/sheath yarn
2.14 Schematic of staple core yarn spinning on a modified ringframe [24].
in response to increasing demand for elastic fabrics and implemented as a result of new technical approaches. The special features of the BT 904 rotor core yarn machine include a filament-core feeding mechanism with the drive easily adjustable by frequency converters up to a 7.0-fold draft, individual sensors and stop device for each filament, modified spinbox, rotor speeds up to 75,000 rpm, delivery speeds up to 150 m/min, IQ Clean® integrated optical yarn clearer system, AMIspin® semi-automatic, electronically monitored piecing system, and yarn connecting unit [26]. Figure 2.15 demonstrates the production of Rotona core spun yarn. The filament enters the spin box through a tube that guides it through the rotor shaft into the centre of the rotor cup. The rotor yarn then wraps around the core. The specially designed technology parts make sure the handling of filament is careful and contact points do not cause any damage. Rotona core yarns in the count range of 5–30 s Ne can be produced from a wide range of raw materials, namely cotton, polyester, viscose as staple fibres, and filaments or elastanes of 10–140 den as core. The machine has a built-in quality monitoring system. Every spinning position is equipped with a filament sensor that stops the spinning process in the case of filament break. The integrated optical yarn clearer IQclean® by
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Table 2.2 Details of various core-spun yarns and fabrics [25] Dyneema-reinforced yarns and fabrics
Fibreglass-reinforced yarns and fabrics
Polyester-reinforced yarns and fabrics
100% cotton
Fibre-glass 100% cotton core
Polyester/cotton 100% cotton (50/50)
Cotton/Dyneema (90%/10%) Core-wrap
Intimate blend
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Warp yarn Count (tex) 42 42 42 33 33 35.8 34.7 Tenacity (g/tex) 15.3 20.1 23.3 14.24 11.45 87 45.9 Weft yarn Count (tex) 39 39 39 45 45 35.8 34.7 Tenacity (g/tex) 14.8 19.2 23.3 12.4 11.91 87 45.9 Fabrics 319 317 325 260 260 264.5 261.7 Grams/m2 (gsm)a Threads/cma 19 ¥ 13 19 ¥ 13 19 ¥ 13 36 ¥ 22 36 ¥ 23 30 ¥ 19 30 ¥ 19 Breaking strength(kg)b 73.6 99.6 114.1 43 36.3 39.6 20.9 Extension at break (%)b 13.9 18.0 20.2 8.5 4.6 20.4 11.9 Tearing strength (kg)b 2.1 3.6 4.6 3.4 3.2 4.32 1.54 Abrasion resistance 212 609 1824 – – – – (cycles)b Char length (cm) 8.4 12.7 11.2 5.5 BELc – – a
Grey state. warp way. c BEL: burnt entire length. b
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2.15 Rotona process for core yarn production [26].
2.16 Structure of Rotona core spun yarn [26].
Rieter controls thick and thin places, moiré effect and yarn count variation. The yarn connecting unit (YCU) identifies and locates the position of the broken yarn. The operator then prepares the yarn end and knotting takes place automatically. The structure of Rotona yarn (Fig. 2.16) is reported to be stable with the yarn (fibres) wrapped around the filament-core. The yarn exhibits greater regularity and reduced hairiness. It is claimed that the Rotona process with a high production rate of 150 m/min and a bigger package (up to 4 kg) containing longer lengths of knot-free yarn is more economical as compared to production of core spun yarns in ring spinning. In addition, the Rotona process sequence is shorter and requires less floor space, labour and power as against the conventional process of core yarn production. The production capacity of the BT 904 Rotona machines, which have been installed for approximately 2 years, is reported to be around 400–500 tonnes per month. Rotona fabrics are currently produced in a number of large, vertically integrated mills in Europe [26].
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2.7.3 Production of core spun yarns in friction spinning Friction spinning stands unique in the production of distinct core–sheath type structures. The core spun yarns can be spun on both DREF 2 and DREF 3 machines, including their latest versions DREF 2000 and DREF 3000 respectively. The details of core yarn production are described at length elsewhere [7].
2.7.4 Production of core spun yarns in air-jet/vortex spinning Murata Machinery, Japan, has developed a core yarn manufacturing device for the production of core spun yarns in air-jet spinning. The filament-core, more commonly Lycra or polyurethane, is drafted to 4–6 times by the positive feed rollers, and covered by sheath fibres such as cotton [27]. The yarn has a twistless core wrapped by sheath fibres. The core is truly coaxial and completely covered in vortex core-spun yarns (Fig. 2.17) and friction-spun yarns as against the ring-spun yarns where it exhibits a barber-pole effect. Core-spun yarns find extensive application in the production of technical yarns such as sewing threads, multi-component yarns, tyre-cord yarns, cable yarns, etc., that are used specifically in the development of flame-retardant textiles, automobile textiles, geotextiles, tents, tarpaulins, abrasives, filtration textiles, etc.
2.8
Wrap spinning
2.8.1 Principle of operation As the name suggests, wrap spinning works on the principle of wrapping. The feed stock, generally a drawn sliver, is drafted in a five-roller drafting system (Fig. 2.18). The drafted strand runs through a hollow spindle without
Vortex core yarn
Ring core yarn
2.17 Structures of vortex-spun and ring-spun core yarns [27].
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2.18 Schematic of Parafil wrap spinning [28].
receiving true twist. A continuous filament yarn, unwound from the bobbin on the hollow spindle, is wrapped helically over the drafted strand of fibres, resulting in a wrap spun yarn. The wrap spun yarn therefore consists of a core of essentially twistless and parallel fibres wrapped helically by a continuous filament (Fig. 2.19). These yarns are also known as ‘cover-spun yarns’ or ‘parallel yarns’, abbreviated to ‘PL yarns’ [7, 28], and the method of spinning is also known as ‘hollow-spindle spinning’. Many manufacturers offer different processes of wrap spinning, but the
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Filament
Staple fibres
2.19 Structure of wrap spun yarn [28].
most commercially successful one is the ‘parafil spinning’ of Spindelfabrik Suessen, Germany. Suessen offers two types of machines, namely [28]: ∑ ∑
Parafil 1000, with medium packages for yarns of 25–100 tex (6–24 s Ne) Parafil 2000, with large packages for yarns of 25–500 tex (1–24 s Ne).
These machines use four- or five-roller drafting arrangements, depending on the raw material to be processed. The Parafil system permits maximum spindle speeds up to 35,000 rpm, and the hollow spindle is designed as a false twisting assembly. The fibre strand does not pass directly after entering the spindle vertically; instead, shortly after entering the spindle, the strand is led out again and back around the spindle with a wrap of about one-quarter of the spindle periphery. In this way, as the spindle rotates, the strand is provided with twist between the drafting arrangement and the head of the hollow spindle. These turns of twist are cancelled out again in the spindle head in accordance with the false twist principle. This twist prevents the strand from falling apart in the length prior to wrapping with filament. Wrapspun yarns are used in the production of furnishings, pile fabrics, upholstery and technical textiles.
2.9
Developing particular yarn properties
There have been many developments in the properties of yarns produced by the popular spinning systems discussed in Sections 2.2–2.8. Such developments
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can be considered under three main headings, namely the role of the raw materials used to build up the yarn, the role of the process parameters that influence the fibre integration in the yarn body and its structure, and ultimately the engineering of yarn for specific applications. All three aspects are discussed below.
2.9.1 Role of raw materials In general, fibres and filaments constitute the raw materials for the manufacture of a yarn. The utility of different types of these fibrous raw materials varies from one spinning system to another and depends upon the specific end uses of the yarn. Table 2.3 highlights the range of fibrous raw materials used on various spinning systems to develop the requisite yarn properties for specific applications. In order to engineer yarns with requisite properties, the various spinning systems prefer the fibrous materials with their properties in order of importance as depicted in Table 2.4.
2.9.2 Role of process parameters It is well known that the process parameters vary from one spinning technology to another. The various process parameters in any spinning system play a decisive role in influencing the yarn structure and hence the properties. Thus Table 2.3 Raw materials used for various spinning technologies Spinning system
Type of raw materials used
Ring spinning (conventional and compact)
All short and medium staple fibres such as cotton, acrylic, polyester, viscose, modal, lyocel, and their blends
Rotor spinning
All short and medium staple fibres such as cotton, acrylic, polyester, viscose and their blends
Friction spinning
Core: (i) staple fibres such as cotton, acrylic, polyester, viscose, kevlar, nomex, trevira; (ii) mono- or multifilaments such as polyester, nylon, polypropylene, aramids, carbon, glass, metallic wires, elastane, etc. Sheath: all staple fibres as in core
Air-jet/vortex spinning
Core: staple fibres such as polyester, viscose, cotton and their blends and elastane Sheath: all staple fibres as in core
Core yarn spinning
Core: all staple fibres, mono- or multifilaments, metallic wires, elastane, etc. Sheath: all staple fibres
Wrap spinning
Core: all staple fibres Sheath: mono- or multifilament
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Table 2.4 Fibre properties for various spinning technologies Spinning system Order of importance of fibre propertiesa
Ring spinning Rotor spinning Friction spinning Air-jet spinning/ vortex spinning Core yarn spinning Wrap spinning a
1
2
3
4
5
Length Strength Friction Fineness
Fineness Fineness Strength Length
Strength Cleanliness Fineness Cleanliness
Friction Length Length Strength
Cleanliness Friction Cleanliness Friction
Fineness Length
Length Fineness
Strength Strength
Friction Friction
Cleanliness Cleanliness
1 = highest order, to 5 = lowest order.
Table 2.5 Specific applications of yarns spun on popular spinning technologies Yarn type
Structure
Specific applications
Ring-spun yarn Homogeneous Apparel, knitted goods, furnishings, high(conventional/compact) quality towels, lingerie, sewing threads Rotor-spun yarn
Bipartite
Denims, jeans, outer garments, terry towels, knitwear, household textiles
Friction-spun yarns
Core–sheath
Technical textiles – fire-retardant textiles, cut resistant fabrics, geotextiles, mobile textiles, composites, conveyors, filters, hoses, ropes, upholstery
Air-jet/vortex yarns
Fasciated
Apparel, curtains, furnishings, hosiery
Core-spun yarns
Core–sheath
Stretch yarns for hosiery, inner garments, medical bandages, sewing threads, sportswear, swimwear and industrial textiles
Wrap-spun yarns
Core–wrapper Cut pile fabrics, blankets, carpets, velours, velvets, furnishings
the important process parameters have to be optimised for the production of the desired quality of yarn. The role of process parameters in various spinning technologies is described in detail elsewhere [7].
2.9.3 Specific applications The development of yarn properties is largely influenced by the specific application(s) of that particular yarn. Hence yarn engineering is of the utmost importance at the present time. Table 2.5 highlights the specific applications of different yarn structures produced using popular spinning technologies. Friction-spun yarns with wide-ranging technical specifications find extensive applications in technical and industrial textiles. Table 2.6 highlights some of the unique technical applications of friction-spun yarns [29].
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Table 2.6 Unique technical applications of friction-spun yarns [29] Yarn type
Yarn count
Core and sheath materials
Properties
Hybrid yarns for 250 tex Core: glass filament reinforced plastics Sheath: polyester
Zero-twisted reinforced filament gives best strength, definable fibre matrix proportion
Hybrid yarns 833 tex Core: none for liquid filter Sheath: pp fibres cartridges
Huddle fibre arrangement for best filter action
Hybrid yarns for 196 tex Core: pp tape secondary carpet Sheath: pp fibres backings (uv stabilised)
Good non-rotting properties, high chemical resistance and good dimensional stability
Hybrid yarns for 125 tex Core: glass filament Flame retardant and high heatproof woven Sheath: para aramid temperature resistance and knitted fabrics Hybrid yarns for 100 tex Core: metallic wire High cut resistance and cutproof woven Sheath: para aramid good dimensional stability and knitted fabrics Hybrid yarns for 250 tex Core: glass filament High yarn volume and good asbestos substitutes Sheath: para temperature resistance aramid/preox fibres
2.10
Yarn texturising: technologies, developments and applications
The word texture refers to the characteristic appearance of a surface having a tactile quality. Texturising is the process of formation of crimp, loops, coils or crinkles in filaments to impart special textures. The texturising process was originally applied to artificial fibres to reduce such characteristics as transparency, slipperiness, and the possibility of pilling (formation of small fibre tangles on a fabric surface). Texturising renders yarns more opaque, improves appearance and texture, and increases warmth and absorbency. Thus texturising is increasingly important in textile production, not only in yarns for weaving and knitting fashion products, but also for carpets, furnishing fabrics and a variety of technical textiles [30].
2.10.1 Prominent yarn texturising technologies Among several texturising methods, false twist texturising and air-jet texturising are very prominent technologies, which are briefly discussed here.
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False twist texturising False twist texturising is a popular method of texturising filament yarns that works on the principle of twist–set–detwist. In this process, a flat filament yarn is twisted, set and untwisted to impart required crimp, stretch and elasticity. When filament yarns made from thermoplastic materials are heat-set in a twisted condition, the deformation of the filaments is ‘memorised’ and the yarn acquires greater bulk. Hence false twist texturising produces very voluminous and highly elastic yarns that find their utility in fashion textiles, tights/stockings and other lingerie as well as in technical end-uses. Air-jet texturising In air-jet texturising, thermoplastic or non-thermoplastic filament yarns are overfed into an air-jet nozzle, wherein the individual filaments with the action of the air-jet get tangled to produce the desired texture. The crimp comes into being through the retraction that happens after the air-mechanical deformation and these yarns exhibit maximum level of bulk as compared to other texturised yarns. With post-thermosetting in a heater the yarn builds up higher crimp stability and reduced shrinkage. A natural, cotton-like look is representative of such yarns. Air-jet texturised yarns are extensively used for home textiles, sportswear for technical applications.
2.10.2 Developments in yarn texturising Developments in false-twist texturising Today, the state of the art in synthetic fibre is in fabric engineering with predefined functions to produce wide-ranging products in accordance with recent fashion trends. Within a single garment there are areas where different yarns are employed for their specific properties. In recognition of these facts, Research Innovation in Textile Machinery (RITM) invested in research to develop new yarn processes, high precision machine components and the never-ending scientific research on surfaces and coatings. For high performance false-twist texturising, RITM has developed a modern false-twist texturising machine, the Goal 1210, with the following features [30]: ∑
∑
Improved thread path with ergonomic creel: Fixed and rotary creels provide well-adapted solutions for low space requirements whilst feeding partially oriented yarn at high speed for standard and delicate low count yarns and microfilaments. Easy threading: The GOAL 1210 FLEX features semiautomatic threading with a pneumatically operated sledge for the primary heater, which presents the yarn to the heater entry.
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∑
Straight yarn path system: RITM has taken the concept of the straight yarn path and applied it to all GOAL 1210 machines. This avoids contact angles, which the delicate yarns cannot stand. The benefit of minimum yarn contact in the texturising zone is that maximum twist passes across the heater, ensuring high bulk levels at maximum yarn tenacity. ∑ False-twist motor spindle: Each false-twist unit is driven by an individual motor and controlled by a common inverter. This ensures that all spindles are controlled at a common rotational speed and deviations between spindles are within acceptable limits for international quality standards. ∑ Contact heater: Vapour phase contact heaters are used for the whole RITM machine range. This system is familiar to all texturising companies and provides a consistent temperature profile across all machine positions, ensuring consistent product quality. ∑ Setting zone: In apparel, the excellent bulk, cover and textile hand that are achieved by the false-twist texturising process are highly desirable. The required bulk level is set into the yarn by overfeeding it into the second heater. This heater also uses the vapour-phase thermosyphon principle. The regular temperature profile ensures consistent treatment from position to position to maintain the consistent bulk achieved during texturising. ∑ Package build: The take-up package winding on RITM’s texturising machinery was developed to create packages with equal density inside and outside and regular density from position to position. The packages are used directly in the next step of operation or can go to yarn dye operations. Following the different technical yarn requirements of each textile application from hosiery to upholstery, from medium count to superfine count, from coarsest to finest micro denier per filament, RITM’s texturising machine range is able to work in the whole range of today’s existing polymer types such as PES, PBT, PTT, PA 6, PA 66, PLA and PP, which can be widely used in woven and knitted fabrics, home furnishings and upholstery [30]. Developments in air-jet texturising In the air-jet texturising process, the compressed air energy must be optimised both to texturise the yarn, and to forward it through the jet. The RITM machines are designed to maximise the available energy, for the benefit of texturising performance. The downward thread path uses the assistance of gravity to feed the yarn through the jet. Prior to the jet, any drag on the yarn due to contact with machine components or changes in direction over ceramic guides is to be avoided. To achieve this, the jet-feed rollers are positioned, relative to the jet, so that no additional guides are required to bring the yarn © Woodhead Publishing Limited, 2010
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to the jet, at the angle recommended by the jet manufacturer. By optimising the process, RITM has achieved significant increase in speed [30]. The AT 8 is an independent-sided, multi-position, line shaft-driven machine of up to nine sections, each with 16 operating positions (eight per side), that offers a perfect process for production of high quality air-jet texturised yarn. The AT 8 has optimum spindle density, giving good ergonomics and maximising process economics. It is best suited to producing yarns in the count range up to 800 dtex where it is well established around the world for apparel production. The shafts are driven by variable-speed AC motors controlled by frequency inverters. All process set points are entered into a central computer, which also monitors machine functions. This machine may be equipped to process fully drawn yarn (FDY) or may be fitted with a draw zone to enable the processing of low oriented yarn (LOY) and partially oriented yarn (POY). The stabilising heater and output feed are automatically threaded, thereby reducing operator load [30]. Air-jet texturised yarns find extensive applications in hosiery for next-toskin wear, sportswear, lingerie, linings, etc. Bulked continuous filament process The bulked continuous filament process, commonly known as the BCF process as shown in Fig. 2.20, has gained prominence in the production of texturised filaments that give rise to bulked staple fibres for the fast-growing fibre-fill and carpet industry. In this process, the crimp in the flat filament yarn is produced largely by asymmetrical quenching or by bi-component Spinning
LD
Drawing
Texturising
Jet type Jet design No. of threads
Interlacing effect
LD32 Open/close 1, 2, 3, 4, 5, 6
Standard tangling
LD4 Open/close 1, 2, 3, 4
High-speed tangling
LD5 Open/close 1
Titre range (dtex)
Cooling Winding
2.20 Schematic of BCF process [31].
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Tangling, commingling 650–10000
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conjugated spinning. The bi-component conjugated fibres are produced either by spinning two polymers differing only in molecular chain length or by spinning two different polymers or copolymers. The crimp in these fibres results from differential shrinkage between the two polymers or their bi-component structure when the resultant fibre is exposed to heat. The low cohesion and high bulk of BCF yarns or cut staple fibres render them preferable in articles such as pillows and furniture back cushions, since it improves refluffability. These yarns also find extensive applications in the manufacture of a wide range of carpets [31].
2.10.3 Technical applications of texturised yarns Texturised yarns are widely applied in technical and semi-technical textile products. The versatility of synthetic fibres such as polyester, nylon and polypropylene renders them suitable for use in texturised form in numerous ways as highlighted below: ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑
texturised microfilament yarns for medical and surgical textiles texturised microfilament yarns for the cleaning sector texturised filament yarns for print base including digital print processes texturised filament yarns for processing in the ribbon industry (decorative ribbons, cable sheathing, etc.) texturised antimicrobial yarns for medicine and hygiene textiles texturised filament yarns as the basis for transdermal patches and bandages texturised filament yarns as core for industrial ropes, cords, hoses, etc. bulked continuous filament yarns for heat bonding, e.g. for insulation and filtration materials, carpet backings, and carpets in the automotive sector.
2.11
Future trends
There has been considerable innovation in yarn spinning processes. Electrospinning and single-step spinning have started making inroads. Future trends include development of spinning technologies for production of nano-yarns, speciality bi-component yarns and intelligent yarns, which will be used to develop smart, intelligent and functional textiles.
2.12
References
1. Stalder H (2000), New spinning process – ComforSpin, Melliand International, 6, 22–25.
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2. Ishtiaque S M, Salhotra K R and Kumar A (2003), Compact spinning: a comprehensive review, Asian Text. J., no. 6, 74–82. 3. www.rieter.com 4. www.suessen.com 5. http://www.textileindustries.com/News.htm?CD=2249&ID=6482 6. http://www.ptj.com.pk/Web%202004/02-2004/rotocraft.html 7. Gowda R V M (2006), New Spinning Systems, 2nd edition, NCUTE, Ministry of Textiles, Government of India. 8. Klein W (1995), New Spinning Systems, vol. 5, Short Staple Spinning Series, Manual of Textile Technology, The Textile Institute International, Manchester, UK. 9. Autocoro 288 Rotor Spinner (2000): customer information brochure, Suessen, Germany. 10. Elsassar N, Braun U and Gries T (2001), Determining optimum strategies for foreign fibre control in spinning, Melliand International, 7, 109–112. 11. Autocoro 360 Rotor Spinner (2004): customer information brochure, Schalfhorst/ Saurer Group, Germany. 12. Eicher E (2001), New R 40 rotor spinning machine – the latest in machine automation, Text. Mag., no. 12, 25–27. 13. Fehrer E (1987), Friction spinning: the state of the art, Text. Month., no. 9, 115– 116. 14. Gsteu M (1982), A spinning process makes the grade, Int. Text. Bull., Spinning, no. 1, 65–82. 15. Fehrer E (1986), Friction spinning: the inventor’s analysis, Text. Month., no. 12, 31–34. 16. www. fehereag.com 17. Ishtiaque S M (1999), Spinner’s attraction at ITMA’99, Asian Text. J., no. 10, 27–32. 18. Basu A (1997), Progress in air-jet spinning, Text. Progress, 29, no. 3. 19. Murata Twin Spinner (2004): customer information brochure, Murata Machinery Ltd, Japan. 20. Chang L and Wang X (2001), The hairiness features of new yarns, Text. Asia, no. 5, 33–35. 21. Artzt P (1999), Short staple spinning on the way to new yarn structures and better raw material utilization, Int. Text. Bull., no. 4, 16–23. 22. http://www.thrc-crhit.org/en/thrcnews/futurtexarchives/2002 23. Oxenham W (2001), Fasciated yarns – a revolutionary development? J. Text. Apparel Tech. Mgmt, 1, issue 2. 24. Sawhney A P S, Robert K Q, Ruppenicker G F, and Kimmel L B (1992), Improved method of producing a cotton covered/polyester staple-core yarn on a ring spinning frame, Text. Res. J., 62, no. 1, 21–25. 25. Sawhney A P S and Ruppenicker G F (1997), Special purpose fabrics made with core-spun yarns, Indian J. Fibre Text. Res., 22, 246–254. 26. www.rotona.com 27. Core Yarn Spinning Device (2004): customer information brochure, Murata Machinery Ltd, Japan. 28. Parafil Wrap Spinning Machines (2002): customer information pamphlet, Spindelfabrik Suessen, Germany. 29. http://www.fischerwolle.com 30. www.ritm-fr.com 31. http://www.patentstorm.us/patents/6492020/description.html © Woodhead Publishing Limited, 2010
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Modification of textile yarn structures for functional applications A. D a s, Indian Institute of Technology, Delhi, India
Abstract: This chapter discusses some of the novel processes of structural modifications, namely bulking, incorporation of micro-pores, twistless and hollow fibrous assemblies, of staple fibre yarns. By modifying the yarn structure the thermophysiological comfort characteristics can be improved by improving the transmission characteristics of heat, moisture and air through the fabric, and the tactile comfort can be improved by proper rearrangements of fibres in yarns and fabrics. The impacts of the structural modifications on characteristics of yarns and fabrics are discussed in detail. Key words: bulk yarn, micro-porous yarn, twistless yarn, hollow yarn, comfort, thermal transmission, moisture transmission.
3.1
Introduction
Different types of staple fibre yarn making processes not only produce different yarn structures but the differences are reflected in the performance of fabrics made from them. Even a staple fibre yarn from a particular spinning process shows altogether different characteristics if the yarn structure is changed. This, in turn, provides more flexibility and more options for textile engineers to change the functionalities of the clothing by changing the yarn structure only. There are various ways of changing the yarn structures, namely by introducing bulk within the yarn, incorporating micro-pores within the yarn structure, removal of one component fibre, chemical treatment, texturing of staple yarns and so on. The fibre packing coefficient plays a significant role through the volume fraction of air in the yarn. The air permeability and thermal conductivity of the fabric depend on the passage of heat, moisture and air through the fabric, which have direct bearing on comfort. So, by changing the packing coefficient of the yarn the transmission characteristics of the fabric, such as air permeability, water vapour transmission rate, thermal conductivity and thermal resistance, can be controlled. The bulking of yarn produces voluminous textiles containing large amounts of air, so that even when they are very light they show very good thermal insulating properties as well as a fuller and agreeable handle. High bulk yarn is produced by shrinkage or contraction of one of its fibre components. Yarn with micro-pores can be 91 © Woodhead Publishing Limited, 2010
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produced by removal of one component from an intimately blended yarn structure. Friction spun yarn is not being used for apparel due to its harsh feel in spite of its many other positive attributes. This harsh feel is due to the wrapper fibres of the sheath which wrap the core to give adequate strength. The harshness can be totally eliminated by structural modification of friction spun yarns. Also, speciality yarn structures, namely twistless or hollow, can be produced with core-sheath type friction spun yarns. Some of the novel processes of structural modification of staple fibre yarns are discussed in this section. Also, the characteristics of these yarns and fabrics made from these yarns are discussed.
3.2
Modifying textile yarn structures by bulking
The bulking of yarn gives a voluminous textile product having good thermal insulation properties as well as a fuller and agreeable handle. Bulked yarns from cotton–synthetic fibre blends are expected to be in good demand for manufacturing diversified products such as apparel including woven and knitted clothing. The principal economic merit of high bulk yarns is the lowering of product weight and consequent saving in textile raw materials. In very low wool blends, the high bulk associated with wool provides the desired wool quality handle and luxurious look to the finished products. On the other hand, the very open structure of these yarns involves an increased risk of pilling and ready soiling, particularly in knitted fabrics, which are typical of synthetics.
3.2.1 Principles of bulked yarn production There are several factors which influence the volume of a yarn, such as the type of its constituent fibres, their number and size, cross-sectional shape, length, the yarn twist, etc. However, the principal factor in yarn bulkiness is the geometric shape and arrangement of the fibres in the yarn. It is known from experience that wool yarns are bulkier than flax or cotton yarns of the same metric count. This is evidently because of the merit of the natural crimp, thickness and length of wool fibres. Though most of the crimp is flattened in the spinning process, it develops again in the dyeing and steaming processes. Any hot wet processing will restore the wool crimp and increase the bulkiness of the yarn. The basic means of developing high bulk yarn is by shrinkage or contraction of one of its fibre components. The process is based on the differential shrinking power of various fibres. In order to obtain the desired bulking effect the difference in the shrinking power of the fibres involved should not be less than 20% [1]. It is, therefore, important that the non-shrinkable fibres
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be stabilized perfectly so as not to shrink at all during the heat treatment processes. On the other hand, the shrinkable fibre component must have a shrinking power of at least 20%. Figure 3.1 shows a schematic diagram of the staple fibre yarn bulking process. The shrinkable (thinner line) and non-shrinkable (thicker line) staple fibres are blended intimately (Fig. 3.1(a)) in the spinning stage. Both fibre components are mixed uniformly in a certain blend ratio and are spun conventionally into yarn (Fig. 3.1(b)). It can be observed from this diagram that the heat provokes contraction of the shrinkable component in the yarn, which migrates to the centre of the yarn (Fig. 3.1(c)). The migration of the contracted fibres to the centre of the yarn is initiated by their considerable shortening. It is known from the theory of yarn structure that the longest fibres assume their position on the surface of the yarn or at the biggest radius, while the shorter fibres tend to move towards the centre of the yarn where they may form theoretically the axis of the yarn. Owing to the shrinkage of the shrinkable fibre components and to their consequent spontaneous migration towards the centre of the yarn, the nonshrinkable fibres will be pushed to the yarn surface where they will form lofty crinkles and loops, thus making the yarn much bulkier. The size of the bulking effect is determined by the difference in the total shrinking power of the fibres in the blend, their relaxation power, the blending ratio and the arrangement of the fibres in the yarn, i.e. by the twist, fibre length, spinning technique, twisting technique, etc. Usually about 40–50% of unrelaxed fibres are blended with 50–60% of pre-relaxed fibres to obtain the best compromise between bulk on the one hand, and shrinkage, strength and elongation at break on the other [2]. The bulkiness increases with increasing content of shrinkable fibres up to 40–50% of the shrinkable component share. In the case of finer fibres (2 to 6 denier) the above proportion is up to a 40% content, and with coarser fibres (6 to 10 denier) it is up to 50% [3]. Any further increase of the shrinkable fibre content does not increase the bulkiness of the yarn, because the number of
(a)
(b)
3.1 Staple fibre yarn bulking process.
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non-shrinkable fibres, which are in fact responsible for the bulk increase, diminishes. It can be said that while the shrinkable fibres provoke the increase in bulk, the non-shrinkable fibres actually make it. The most popular yarns produced with the above technique are the acrylic bulk yarns. The shrinking power is imparted to acrylic fibres in the form of tow by hot stretching on a tow-to-top converter machine. It is, however, possible to use to advantage the shrinking power of other artificial fibres such as PVC or polyester. One of the newer developments is bulk yarns made of polyester fibres. This is, in fact, a modified polyester fibre, which due to an added component has acquired the desired shrinking power in a hot environment. The non-shrinkable component may be natural or artificial fibres whose shrinkage lies below 1%. The shrinkable and non-shrinkable fibre blended yarns can be processed by any of the following three techniques to develop high bulk in the final products: ∑
The bulk is developed in the yarn form, usually in hank form, and the bulked yarn is then converted into knitted and woven textile products. ∑ The blended pre-bulked yarn is processed by conveniently adapted methods into knitted and woven fabrics and the bulk is developed in fabric form (in the course of the dyeing process). ∑ The blended pre-bulked yarn is processed by conveniently adapted methods into knitted or woven piece goods or semi-products and the final bulk is developed in piece good form. Each of these techniques has its advantages and drawbacks. The technically most exacting is the production of textile goods of high bulk yarns which were shrunk in hank form. The other two techniques are economically attractive but from the viewpoint of quality they do not always give full satisfaction, with the exception perhaps of middle-wear produced on full-fashioned knitting machines, jerseys and ladies’ dress goods [3].
3.2.2 Bulking of ring spun yarns The bulked yarns produced by shrinkage of one fibre component in the yarn differ from other yarns not only in structure but also in their bulk, mechanical and surface properties. The properties of fabrics produced from these yarns are affected by such yarn properties as well as by their fabric construction parameters. The properties of fabrics made of bulked yarns are different from those of normal yarn fabrics in all respects. It is known that bulked yarns are different from normal ring yarns in the free state; this affects the fabric structure and this is reflected in the behaviour of the fabrics. The bulking of yarn gives a voluminous textile product having good thermal insulating properties as well as a fuller, agreeable handle. The properties of fabrics
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produced from these yarns are affected by such yarn properties as well as by their fabric constructional parameters. Yarn characteristics The presence of shrinkable fibre in the blend results in significant shrinkage in the yarn. The increase in yarn twist results in an increase in yarn shrinkage; this may be due to a higher inter-fibre contact force at higher twist levels causing reduction in slippage between fibres during shrinkage of the shrinkable component and leading to an increase in effective yarn shrinkage. The bulking treatment increases the diameter of the yarn as well as the specific volume of the yarn significantly. In general, the tenacity of yarn increases after bulking. The effective yarn twist per unit length increases after the bulking process, which may be one of the causes of increased tenacity after bulking. Another possible cause may be the removal of natural oils, fats and waxes during the boiling treatment, which possibly increases the inter-fibre friction for cotton/nonshrinkable acrylic blended normal yarns [4]. The breaking extension after bulking increases tremendously [5]. This is mainly due to the shrinkage of the yarn and the buckling of the cotton component during the bulking treatment. More shrinkable acrylic fibres in the blend tend to have more yarn shrinkage and result in a high breaking extension. The initial modulus of blended yarn before bulking is higher than that of 100% cotton yarn for the same count, but after bulking it is reduced. As the specific volume of the yarn increases due to buckling of the cotton fibres, the yarn becomes more pliable in its initial zone of the tensile curve. Thus bulked yarns initially extend very easily. The bulking treatment reduces the flexural rigidity of yarns significantly, since it causes disorientation of the structure of the yarn which results in lowering of the yarn flexural rigidity. The wicking height of bulked yarn is higher than that of the 100% cotton yarn sample, because after bulking more capillary space is created within the yarn. Coarser count yarns give more wicking height than finer ones, which may be due to the presence of more capillary spaces [6]. Fabric characteristics In a study by Das et al. [7], bulking treatment reduced the breaking load of all the fabric samples considerably, and the 100% cotton fabric showed a much higher breaking load. The breaking extension of fabrics produced from bulked yarns is more than that of 100% cotton fabric. The initial moduli of bulked fabrics are substantially reduced due to bulking. The crease recovery angle of fabric with bulked yarn is, in general, higher than that of 100% cotton fabric. Fabrics made of bulked yarns show higher abrasion resistance
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than 100% cotton fabric. Bulked yarns are loose in structure and can flex easily during abrasion and thus absorb more abrasion energy than compact fabrics. Also, the presence of an acrylic component in bulked yarns results in higher abrasion resistance. The bending rigidity of fabrics made of bulked yarns is lower, due to the reduction in the compactness of the yarn assembly after bulking, which helps to give easier movement of the individual fibres in the bulked weft yarns during bending or flexing of the fabric. Bulked yarn fabrics show lower compressional energy and better recovery than 100% cotton fabrics. Bulked yarn fabrics also show lower thermal conductivity than 100% cotton fabrics, which may be attributed to the very bulky structure of the weft acting as an insulating medium, trapping air in the loose fibrous assembly spaces and not allowing the heat of the inner layer to be transmitted to the outer layer. Moisture vapour transmission (MVT) is an important parameter in evaluating the comfort characteristics of a fabric, as it represents the ability to transfer perspiration from the body. The moisture vapour transmission rate (MVTR) values of bulked yarn fabrics are higher than that of 100% cotton fabric. Since yarn structure plays an important role in the transmission of water vapour, the open structure of bulked yarn has a better cover factor, which allows water vapour to be transferred from inside to outside through diffusion. The wicking rate is lower in bulked yarn fabrics than in normal fabric. Since the pores in bulked yarns are distributed in a random fashion, there is no proper channel or capillary for the water to pass through, so the pores have the capability of holding the water inside, which reduces the transmission rate.
3.2.3 Bulking of yarns of different spinning technologies In a study carried out by Das and Mal [8], different spinning technologies with different proportions of shrinkable fibre core in the core-sheath of DREF-III yarns showed a significant impact on various properties of cotton–acrylic blended bulked yarns and fabrics. For all the yarns, after boiling treatment, there was a lengthwise shrinkage and an increase in specific volume. The percent shrinkage of ring and rotor yarns was almost the same, whereas the DREF-II yarn showed less shrinkage [8]. In Group A, cotton–acrylic intimate-blended yarns were produced in three different spinning systems (ring, rotor and DREF-II). In Group B, cotton–shrinkable acrylic core-sheath type yarns were made from the DREF-III system by changing the shrinkable acrylic fibre percentage in the core. Cotton fibre was used in the sheath. The following were the proportions used: ∑ ∑
50% acrylic fibre in core and 50% cotton in sheath 60% acrylic fibre in core and 40% cotton in sheath
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70% acrylic fibre in core and 30% cotton in sheath 100% cotton fibre (60% core in core-sheath structure).
Yarn characteristics It is observed that in all the yarns, the general trend is that after boiling treatment there is a lengthwise shrinkage of yarns and the specific volume also increases. This indicates that there is increase in bulk of all the yarns, although the extent is different for different yarns. The relative shrinkage of the ring and rotor yarns is almost the same whereas the DREF-II yarn shows less shrinkage [8]. The specific volume of ring spun yarns before bulking is lowest, followed by the rotor yarn, with the DREF-II yarn showing the highest specific volume (Fig. 3.2). But in the case of ring spun yarn the percentage increase in specific volume is maximum among the three spinning systems. This may be due to the fact that in ring spun yarns the fibres are aligned in a certain helical fashion along the axis of the yarn, which in turn helps in bulking of the yarn structure during shrinkage of shrinkable-acrylic yarn. In case of core-sheath type DREF-III yarn (Group B), with the increase in the proportion of shrinkable acrylic core in the yarn from 50% to 60%, the yarn shrinkage increases marginally but after that there is no further change. But as far as the percentage increase in specific volume is concerned, initially there is a steep increase when the proportion of shrinkable acrylic core in the yarn increases from 50% to 60%, but after that it drops as the proportion of shrinkable acrylic core in the yarn increases from 60% to 70% (Fig. 3.3) [8]. The initial increase in specific volume is mainly due to an increase in the bulking force as a result of a higher proportion of shrinkable acrylic core, but then as the shrinkable acrylic core increases the cotton sheath component, which is the buckling component to develop bulk in the yarn, reduces and this results in less bulking of the yarn. Moreover, as the cotton
Specific volume (cm3/g)
4
Before bulking After bulking
3.5 3 2.5 2 1.5 1 0.5 0
Ring
Rotor Spinning system
DREF
3.2 Change of specific volume after bulking of yarns of different spinning technologies.
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Specific volume (cm3/g)
3.5 Before bulking After bulking
3 2.5 2 1.5 1 0.5 0
50%
60% 70% 100% cotton % Shrinkable acrylic in core of dref-III yarn
3.3 Change of specific volume after bulking of core-sheath yarn. 12
Before bulking After bulking
Tenacity (g/tex)
10 8 6 4 2 0
Ring
Rotor Spinning system
DREF-II
3.4 Change of tenacity after bulking of yarns of different spinning technologies.
component reduces it will offer less resistance in shrinkage, thus resulting in a reduction in bulkiness. It can be observed from Fig. 3.4 that the tenacity of all the yarns of Group A increases after bulking, whereas in case of core-sheath type DREF-III yarns (Group B yarns) there is a significant drop in tenacity (Fig. 3.5). The increase in tenacity after the bulking treatment may be due to the shrinkable acrylic fibres gripping the fibre strands more tightly, leading to increased inter-fibre friction and resulting in resistance to inter-fibre slippage. It also increases the effective twist per unit length of the yarn. The drop in tenacity of DREF-III yarns may be due to shrinkable acrylic fibres present in the core shrinking during heat treatment, and the maximum strength of core-sheath type DREF-III yarn depends on the parallel core fibres and proper gripping of the sheath fibres which bind the core fibres. The shrinkage of the core fibres results in disorientation of the structure as a whole, and the binding strength of the sheath fibres also decreases, resulting in a decrease in yarn strength.
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56 54 52 50 48 46
50% 60% 70% % Shrinkable acrylic in core of Dref-III yarn
3.5 Change of tenacity after bulking of core-sheath yarn.
The flexural rigidity of the yarns reduces after bulking treatment, due to disorientation of the structure of the yarn during shrinkage of the acrylic component. The compressibility of all the yarns increases after bulking, mainly because during bulking treatment the specific volume of all the yarns increases, which results in the creation of air spaces inside the yarn structure, leading to increase in compressibility. The percentage recovery of all the yarns after bulking increases, mainly due to higher recovery of buckled cotton fibres in bulked yarns [8]. Fabric characteristics The bulking treatment reduces the breaking load of all the fabric samples considerably, and the 100% cotton fabrics show a much higher breaking load than the corresponding cotton–acrylic blended bulked fabrics. This trend is true for all the yarn technologies. This may be due to the fact that during bulking treatment the yarn shrinks, and the shrinkage behaviour of yarns is not uniform, i.e. the levels of shrinkage of yarns are not the same. So, during fabric tensile testing the breaking extension of individual yarns varies, resulting in unequal load sharing between the yarns making up the fabric. As a result, the yarns break at different times, resulting in a lower breaking load of the overall fabric [9]. The breaking load of fabrics from bulked yarns is lower than that of 100% cotton reference DREF-III yarn fabric, and the breaking elongation of these bulked yarn fabrics is much higher than that of the reference 100% cotton DREF-III yarn fabric. The higher breaking elongation of bulked yarn fabrics is mainly due to shrinkage of the yarns during the bulking treatment, and the drop in breaking load is mainly due to unequal load sharing of the component yarns and fibres. Fabrics made of bulked yarns in weft show higher abrasion resistance than the corresponding 100% yarn cotton fabrics. Bulked yarns are loose in structure and can flex easily during abrasion, thus absorbing more abrasion energy than normal yarn fabrics. The crease recovery angle (CRA) and the compression of fabrics made from bulked yarns are higher than those of the
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corresponding 100% cotton yarn fabrics. These trends are valid for yarns made from all the different technologies [9]. All the fabrics from bulked yarns show less air permeability than the corresponding 100% cotton fabrics. This is mainly due to the greater diameter of bulked yarns as compared to 100% cotton yarn, which results in less interyarn space. Bulked yarn fabrics also show higher thermal resistivity than the corresponding 100% cotton fabric, which may be attributed to the very bulky structure of the weft which works as an insulating medium. The MVTR values and the vertical and horizontal wicking of fabrics from bulked yarns are greater than those of the corresponding 100% cotton yarn fabrics [9].
3.3
Modification of textile yarn structures by incorporating micro-pores
Structural modification of yarns can also be carried out by incorporating additional micro-pores inside the yarn body in addition to the existing micropores. This increases the porosity of the yarn and hence improves some of the desirable characteristics of yarns and fabrics.
3.3.1 Principles of micro-porous yarn production Micro-pores are incorporated within the yarn body by dissolving one of the fibre components from the yarn structure. To obtain micro-porous cotton yarn the cotton–PVA blended yarn samples are prepared in a cotton ring spinning system. Cotton and PVA staple fibres are blended in the blow room of the cotton spinning system with different blend ratios, depending on the requirement. PVA, being water soluble, is removed when the PVA blended yarn (Fig. 3.6(a)) is washed in warm water, leaving voids within the yarn body (Fig. 3.6(b)). To create micro-pores within the structure of yarns by dissolving PVA fibre, the yarns in the hank form are immersed in plain water at 70ºC temperature for 20 min with constant stirring. Then the hanks are taken out
water-soluble fibre (a)
Void
3.6 Creation of micro-pores within the yarn body.
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and washed thoroughly in cold water, dried in an oven at 105ºC for 2 hours and then conditioned for 24 hours in standard atmospheric conditions to get a standard moisture content. Proper care should be taken for complete removal of the PVA component from the structure, i.e. the hanks should be properly opened, the water temperature should not drop below 70ºC and constant stirring should be maintained throughout the dissolution process.
3.3.2 Yarn properties The linear density of micro-porous yarns is finer than that of the corresponding parent yarn, due to the removal of the PVA component from the yarn. The specific volume of micro-porous yarns is higher than that of the parent yarn due to the presence of voids within the yarn body. There is a reduction in yarn tenacity after the incorporation of micro-pores with the yarn body. The yarn compressibility increases significantly after the wash, due to the removal of the PVA component from the yarn structure resulting in micro-pores within the yarn structure [10].
3.3.3 Fabric characteristics The initial modulus reduces with the increase in the proportion of micropores within the yarn structure. This may be due to the presence of micropores within the twisted yarns resulting in significant change in stress–strain characteristics at lower stress levels. The incorporation of micro-pores in the yarn structure results in an increase in fabric abrasion resistance. This may be because of the fact that yarn with more micro-pores is more flexible with a lower packing factor. This type of structure absorbs much of the abrading force and hence shows more abrasion resistance. The bending rigidity of a fabric reduces significantly when micropores are incorporated within the yarn structure, because the creation of micro-pores in the yarn makes the yarn more flexible and more easily bent during the exertion of a load. The incorporation of micro-pores in the yarn structure results in an increase in fabric compressibility and a reduction in compressional energy, because the removal of water-soluble PVA fibres makes the yarn porous and hence the fabrics more compressible. The reduction in compressional energy with increase in the level of PVA content is mainly due to the fact that a higher PVA content in the yarn makes the yarns and fabrics more porous and thus easily compressed even at lower pressure, resulting in lower compressional energy [11]. The compressional resiliency reduces with increase in micro-pores. As the number of micro-pores in the yarn increases there is a decrease in the air permeability of the fabric. This is mainly due to the higher compressibility of the yarn with more micro-pores resulting in a flattening
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of the yarns and the covering of more inter-yarn space in the fabric. Also, yarns with more micro-pores are more bulky, resulting in less inter-yarn space than in relatively compact yarns for the same thread density. Fabrics with micro-pores in the yarn have lower thermal conductivity than 100% cotton reference fabric samples, because the removal of PVA fibres creates micro-pores within the yarn structure, resulting in more entrapped air. Since air is a poor conductor of heat as compared to fibre, there is less transmission of heat through the fabric. The moisture vapour permeability of the fabric is a critical property for clothing systems that must maintain thermal equilibrium for the wearer. Fabric samples with micro-pores within the yarn structure show higher MVTR values than reference fabrics from 100% cotton normal yarn [12]. The increase in the moisture vapour transmission rate with increase in the PVA content is due to better exchange of water molecules in vapour form between two faces of the fabric. The micro-pores assist in the transfer of water particles in vapour form from one to the other by diffusion through them.
3.4
Twistless and hollow yarns
Friction spun yarn is not used for apparel due to its harsh feel, in spite of its many other positive attributes. This harsh feel is due to the wrapper fibres of the sheath which wrap the core to give adequate strength. Therefore removal of the sheath or core is sought by incorporating water-soluble PVA, without compromising the basic quality requirements of the fabrics and the physiological comfort-related properties affecting the transmission behaviour of fabrics made of modified yarn, viz. thermal conductivity, air permeability and water vapour permeability.
3.4.1 Principles of production Twistless and hollow yarns are developed by modifying core-sheath type friction spun yarns produced in the DREF-III spinning machine [12]. To obtain a twistless yarn structure, the sliver of insoluble fibre component, e.g. viscose fibre, is placed in the core and slivers with PVA fibre are placed in the sheath of core-sheath type friction spun yarn (Fig. 3.7). To produce hollow yarn the placement of the viscose and PVA slivers is simply reversed, i.e. the PVA sliver is placed in the core and viscose slivers are placed in the sheath (Fig. 3.8). To segregate the individual core and sheath components in DREF-III friction spun yarn, the PVA fibres must be removed from the yarn body and the viscose fibres should remain either in the core or in the sheath. PVA is soluble in water at 70oC, and the dissolved PVA should be removed
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Staple PVA Staple viscose
3.7 Core-sheath type DREF-III yarn for twistless structure.
Staple viscose
Staple PVA
3.8 Core-sheath type DREF-III yarn for hollow structure.
from the yarn body properly. To avoid any entanglement or distortion of the structure during the PVA extraction process, the friction spun yarns are wrapped carefully on perforated plastic cheeses. Sufficient care should be taken during wrapping to avoid any overlap of the yarn which may affect the proper extraction of PVA. The cheeses are then dipped into boiling water for about 15 minutes and then shaken in hot water followed by cold water.
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3.4.2 Yarn properties
Stress
Figures 3.9, 3.10 and 3.11 show the typical stress–strain curves of parent DREF-III yarn, twistless yarn and hollow yarn, respectively. In parent
0
Strain
Stress
3.9 Typical stress–strain behaviour of parent DREF-III yarn.
0
Strain
Stress
3.10 Typical stress–strain behaviour of twistless yarn.
0
Strain
3.11 Typical stress–strain behaviour of hollow yarn.
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DREF-III yarn, the sheath fibres create the transverse force to hold core fibres together. When the yarn extends, the core fibres are exposed to most of the stress initially. Therefore, breakage might start from the core section and move quickly through the wrapper section. The stress–strain curves of parent DREF-III yarn, twistless yarn and hollow yarn are different from each other. The curve for twistless yarn shows an initial very steep rise and then a sudden fall in the stress value followed by stick-slip movement of the curve (Fig. 3.10). The initial portion is due to more axially oriented fibres and the stick-slip zone is the result of fibre-to-fibre slippage in the core component due to the very low twist present in the core. The load–elongation curve for hollow yarn (Fig. 3.11) shows no such steep rise in stress at the initial stage and the curve is not smooth throughout. This may be due to the fact that in the absence of a core component when stress is being applied on the hollow sheath component, reorientation of the structure may be taking place by slipping and re-locking within the sheath fibres. The breaking elongation of hollow yarn is of a similar magnitude to that of the parent DREF-III yarn, whereas the twistless yarn breaks almost immediately [12].
3.4.3 Fabric properties The mechanical properties of fabrics made of twistless and hollow yarns in weft are given in Table 3.1. The tensile strength of fabrics with twistless yarn is found to be the highest [13]. This may be due to the fact that the compacting forces created in the fabric structure itself result in higher inter-fibre frictional force. Also, the parallel fibres in twistless yarns along the load direction result in uniform and maximum load sharing by all the component fibres of the fabric. The presence of minimum tensile strength in the weft direction of hollow yarn fabric is due to the fact that in the hollow yarn most of the fibres are not aligned to the axis of the yarn. The hollow sheath component is of wrapper fibres which wrap around the core component. The effective length of fibres along the yarn axis is very small and also the fibre migration within the hollow yarn structure is almost negligible, which results in poor strength of fabric. Fabric with hollow yarn shows multi-stage breakage. After reaching a maximum load value, structural reorientation in the weft yarns inside the fabric takes place, resulting in more than one peak. It is also clear from Table 3.1 that the tear strength of fabric made with twistless yarn is higher than that of fabric from parent yarn, whereas fabric with hollow yarn shows the lowest tear strength. The tear strength mainly depends on the yarn strength, the fabric structure and the surface characteristics of the yarn. Apart from these, the alignment of the fibres in the yarn also plays an important role. Yarns bridge the delta zone at the point of tear, and the tightness of the fabric structure determines how many yarns carry the load. A tight fabric allows only one yarn to break at a time as the tear
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Yarn type
Tensile Breaking Tear strength, Flexural rigidity, Crease recovery, Compression, Abrasion resistance strength, N elongation, % N mN.mm2/mm deg % cycles
Parent DREF-III yarn
382.9
22.48
30.64
13.28
83
15.0
231
Twistless yarn
439.2
24.30
36.77
9.97
103
17.4
250
Hollow yarn
146.6
17.64
16.73
6.67
98
21.3
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Table 3.1 Mechanical properties of fabrics
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propagates. A loose fabric allows more yarns to carry the load at any one time. Table 3.1 shows that the flexural rigidity of fabric made with twistless yarn is higher than that of fabric with hollow yarn. This result would seem to be odd as the hollow yarn is expected to show higher flexural rigidity. The deviation from what might be expected can be related to the partial flattening of hollow yarn and also the alignment of fibres. Moreover, the parallel alignment of fibres in twistless yarn develops some restrictive force during bending. The maximum weft flexural rigidity of parent yarn fabric is due to compact weft yarn. It is evident from Table 3.1 that the crease recovery of fabrics made from twistless and hollow yarns is higher than that of fabric with parent yarn. The compression of fabric with hollow yarn is maximum, followed by fabric with twistless yarn and fabric with parent yarn, the difference being due mainly to the different structure of the yarns. The abrasion resistance of fabric with twistless yarn is higher than that of fabric with parent yarns, which in turn is higher than that of fabric with hollow yarns, due to the particular wrap structure of the sheath component in weft yarn. Woven fabrics made from staple twistless and hollow yarns have a great impact on properties related to comfort, i.e. air permeability, thermal conductivity, percentage water vapour permeability, wicking and water absorbency. Woven fabric with twistless yarn shows higher air permeability than the corresponding fabric with hollow yarn (Fig. 3.12). Diameter, structure and crimp of the yarn and flattening of the fibrous structure affect the air permeability of a fabric. The very low air permeability of hollow yarn fabric may be attributed to its very bulky structure resulting in blocking of the inter-yarn spaces. For the same yarn linear density the effective diameter of hollow yarn is higher than that of twistless yarn. Blocking of inter-yarn spaces may also be due to partial flattening of the
Air permeability (cm/s/cm2)
60 50 40 30 20 10 0
Parent yarn
Twistless yarn Type of yarn in fabric
3.12 Air permeability of fabrics.
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hollow structure after removal of the core component resulting in reduction of air permeability. Twistless yarn has higher inter-yarn space due to its compact packing which in turn leads to higher air permeability. Fabric made of parent DREF-II yarn shows maximum thermal conductivity, and fabric made with hollow yarn shows minimum thermal conductivity (Fig. 3.13). Fabric with twistless yarn has intermediate values of thermal conductivity. The low value for hollow yarn is due to the very bulky structure of the hollow fibrous assembly in weft acting as an insulating medium. It entraps air in the hollow spaces and does not allow the heat of the inner layer to transmit to the outer layer [14]. Water vapour permeability is an important parameter in evaluating the comfort characteristics of a fabric, as it affects the ability to transfer perspiration from the wearer’s body. Fabric made of hollow yarn has the highest water vapour permeability, whereas fabric with twistless yarn has the lowest capability and fabric made of parent DREF-III yarn has intermediate values for permeability (Fig. 3.14). The very high water vapour permeability of fabric with hollow yarns is attributed to the very bulky structure of hollow yarn. Yarn characteristics play an important role in transmission of water vapour. An open structure allows more water transmission. Hollow yarns have a better cover factor, which allows water vapour to transfer from the inside to the outside through diffusion. The wicking property of a fabric mainly depends on the characteristics of the fibre and the structure of component yarns and the fabric. Fabric with twistless yarn has the highest wicking value followed by fabric with hollow yarns, and fabric with parent DREF-III yarn shows the lowest wicking. Twistless yarns, due to their more parallel fibres, smaller pores and definite channels, wick more water through capillary pressure. Small, uniformly distributed and interconnected pores and channels facilitate fast liquid transport [14].
Thermal resistance (tog)
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
Parent yarn
Twistless yarn Type of yarn in fabric
3.13 Thermal resistance of fabrics.
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Relative water vapour permeability (%)
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108 104 100 96 92 88
Parent yarn
Twistless yarn Type of yarn in fabric
Hollow yarn
3.14 Water vapour permeability of fabrics. 145
Water absorbency (%)
140
135
130
125
120
Parent yarn
Twistless yarn Type of yarn in fabric
Hollow yarn
3.15 Water absorbency of fabrics.
The water absorbency of a fabric mainly depends on the moisture regain of the component fibre and the open space within the fabric structure and is an indication of the sweat-holding capacity of the fabric. The fibre components in all three fabrics are exactly the same, so the amount of voids within the structure of the fabric plays an important role in water absorbency. Fabric with hollow yarn shows the highest water absorbency, whereas fabric with twistless yarn has the lowest water absorbency (Fig. 3.15). The very high value for hollow yarn fabric may be attributed to the very bulky structure of the hollow fibrous assembly. The water replaces the air in the hollow fibrous assembly and thus it can hold more water. On the other hand, fabric with twistless yarn shows the least water absorbency, which may be due to the fact that the compact and parallel aligned twistless fibrous assembly does not have sufficient open space to hold extra water.
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Future trends
The yarns produced from different spinning technologies have their own limitations. Except for ring spun yarns, the yarns from the other spinning technologies are generally not suitable for use in apparel, mainly because of the arrangement of fibres within the yarn body. These yarns can be made useful for apparel applications if their structures can be changed. Minor structural changes during the spinning process are possible to some extent by changing the spinning parameters, but significant changes in the structural characteristics of these yarns are possible only by modifying the yarn manufacturing process or by after-treatment. Such structural changes in these yarns are necessary for wider applicability and improved performance. The comfort characteristics of fabrics depend on the structure and types of yarn used among other factors. The development of new yarn structures raises questions about the nature and quality of fabric made from these yarns. The tendency to increase the yarn volume or porosity as much as possible may be traced back to the finding that revealed the relationship between the volume of a textile product and its thermal insulating properties, handle and covering power. It was found that voluminous textiles contain large amounts of air so that even with very light weight they show very good thermal insulating properties and a fuller and more agreeable handle. This is evidently due to the merit of the natural crimp, thickness and length of wool fibres. Though most of the crimp is flattened in the spinning process, it develops again in the dyeing and steaming processes so that the comparatively lower voluminosity of grey wool yarns is not typical. Any hot wet processing will restore the wool crimp and increase the bulkiness of the yarn. The principal economic merit of high bulk yarns is the lowering of product weight and consequently the saving in textile raw materials of the order of 10% and more. In very low wool blends, the high bulk of wool provides the desired wool quality handle and luxurious look to the finished products. On the other hand, the very open structure of these yarns involves increased risk of pilling and ready soiling, particularly in knitted middle-wear, which are typical of synthetics. Furthermore, in order to assert the advantage of high bulk or porous products it is necessary to instruct their users properly on their maintenance by attaching convenient instruction labels to the products. In comparison to woollen products, the products made of high bulk yarns show better performance characteristics, particularly non-felting properties and shape retention.
3.6
References
1. B. Piller, 1973, Bulked Yarns, Textile Trade Press, Manchester, UK, pp. 156–210. 2. E. Oxtoby, 1987, Spun Yarn Technology, Butterworth, London. 3. B. Banerjee, 2007, Study on the characteristics of needle-punched nonwoven fabrics
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4.
5. 6.
7.
8.
9.
10.
11.
12.
13.
14.
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made from blends of shrinkable and non-shrinkable acrylic, M. Tech. thesis, Indian Institute of Technology, Delhi. G. K. Tyagi and S. Dhamija, 1998, Variation in the characteristics of acrylic–cotton ring and OE rotor yarns as a consequence of steam-relaxation treatment, Indian Journal of Fibre and Textile Research, 23(3), 136–140. A. K. Sinha and G. Basu, 2001, Studies on physical properties of jute–acrylic blended bulked yarns, Indian Journal of Fibre and Textile Research, 26(3), 268–272. A. Das, V. K. Kothari and M. Balaji, 2007, Studies on cotton–acrylic bulked yarns and fabrics: Part I – Yarn characteristics, Journal of the Textile Institute, 98(3), 261–267. A. Das, V. K. Kothari and M. Balaji, 2007, Studies on cotton–acrylic bulked yarns and fabrics: Part II – Fabric characteristics, Journal of the Textile Institute, 98(4), 363–375. A. Das and R. D. Mal, 2009, Studies on cotton-acrylic bulked yarns produced from different spinning technologies: Part I – Yarn characteristics, Journal of the Textile Institute, 100(1), 44–50. A. Das, M. Zimniewska and R. D. Mal, 2009, Studies on cotton–acrylic bulked yarns produced from different spinning technologies: Part II – Fabric characteristics, Journal of the Textile Institute, 100(5), 420–429. S. M. Ishtiaque, A. Das and R. P. Singh, 2008, Packing of micro-porous yarns: Part I – Optimization of yarn characteristics, Journal of the Textile Institute, 99(2), 147–155. A. Das, S. M. Ishtiaque and R. P. Singh, 2009, Packing of micro-porous yarns: Part II – Optimization of fabric characteristics, Journal of the Textile Institute, 100(3), 207–217. A. Das, S. M. Ishtiaque and P. Yadav, 2004, Contribution of core and sheath components in the tensile properties of DREF-III yarn, Textile Research Journal, 74(2), 134–139. A. Das, S. M. Ishtiaque and P. Yadav, 2003, Properties of woven fabrics containing core-sheath DREF-III yarn in weft, Indian Journal of Fibre and Textile Research, 28(3), 260–264. A. Das and S. M. Ishtiaque, 2004, Comfort characteristics of fabrics containing twist-less and hollow fibrous assemblies in weft, Journal of Textile and Apparel Technology and Management, 3(4), 1–7.
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4
Yarn hairiness and its reduction
A. M a j u m d a r, Indian Institute of Technology, Delhi, India
Abstract: This chapter presents an overview of spun yarn hairiness and its reduction. First the factors influencing yarn hairiness are discussed. Then the different hairiness testing and evaluation methods are compared. The importance of yarn hairiness from spinning, weaving, knitting and fabric quality viewpoints is incorporated, and yarn hairiness modelling is discussed in brief. Finally, the manufacturing methods and systems for yarn hairiness reduction are covered in detail with special focus on compact spinning, jetring and jet-winding technologies. Key words: compact spinning, hairiness testing, hairiness modelling, jetring, jet-winding.
4.1
Introduction
Yarn hairiness, one of the most important yarn parameters, is usually characterized by the amount (number or cumulative length) of fibres protruding out of the compact yarn body. In a spun yarn, the majority of the fibre ends are embedded in the main structure, although a few ends may protrude out as a consequence of their shorter length or higher bending and torsional rigidities. Hairiness could broadly be classified under three categories, namely leading hairs, trailing hairs and looped hairs. Yarn hairiness has a great influence on the sizing, weaving and knitting processes (Barella, 1983, 1993, 1997). Higher hairiness increases the cost of sizing. During the shedding operation in weaving, the hairy yarns often entangle with each other and thus hinder the creation of distinct shed which is essential for the passage of the weft or weft carrier. In case of air-jet weaving, the yarn hairiness favourably influences the air-drag exerted on the yarns. Hairy yarns generate fly during the knitting and obstruct the smooth functioning of the machine parts, including needles. Excessive variation of yarn hairiness may cause a ‘Barre’ effect in the finished fabric. However, yarn hairiness is a necessary evil. Too much hairiness is detrimental for the fabric appearance but a certain hairiness in the yarn is also desired so that the fabric possesses a softer feel and a warmer hand. It has been observed that the comfort parameters of textile fabrics (air permeability, moisture vapour transport and thermal properties) depend on yarn hairiness. Therefore, textile researchers have thoroughly investigated the role of fibre and process parameters in the 112 © Woodhead Publishing Limited, 2010
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generation of yarn hairiness and the ways to curb the problems associated with excessive hairiness.
4.2
Factors influencing yarn hairiness
4.2.1 Fibre-related factors of yarn hairiness The following fibre-related factors influence the hairiness of spun yarn significantly: ∑ Torsional and flexural rigidities ∑ Fibre length and short fibre content ∑ Fibre fineness. Several studies have been conducted by researchers (Pillay, 1964a,b; Zhu and Ethridge, 1997; Atlas and Kadoglu, 2006) to elicit the relationship between the fibre parameters and yarn hairiness. Torsional and flexural rigidities A fibre becomes hair when it escapes the twisting action of spinning machines by virtue of its higher torsional and flexural rigidities. Pillay (1964a) found that the torsional rigidity of cotton fibre is the most important parameter influencing yarn hairiness. He reported that flexural rigidity and mean fibre length are the parameters in the order of influence after the torsional rigidity. Considering the fibre to be a cylindrical rod, the torsional rigidity and flexural rigidity can be expressed as follows:
Torsional rigidity =
p h d4 32l
Flexural rigidity = EI = E
p d4 64
where h is the rigidity modulus, E is Young’s modulus, I is the area moment of inertia, d is the diameter and l is the length of the fibre. Fibre length and short fibre content For a given mass of fibre, the number of discontinuous ends will be less if the mean fibre length is high. Besides, longer length reduces the torsional rigidity of the fibre. Thus yarns spun from longer fibres are less hairy. Short fibres have fewer contact points with the other fibres. Moreover, they have a preferential migration towards the surface of the yarn. Therefore, short fibres are prone to protrude out of the yarn body, causing hairiness.
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Fibre fineness As the torsional and bending rigidities of circular fibres are proportionate to the fourth power of the radius, finer fibres could be laid on the yarn body very easily due to the lack of resistance against torsion and bending. Thus finer fibres produce less hairy yarns than the coarse fibres if the twist level in the yarn is the same.
4.2.2 Process-related factors of yarn hairiness The following process-related factors influence the hairiness of spun yarn significantly: ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑
Spinning technology Winding operation Blending and mixing Combing operation Number of drawframe passages Roving fineness and twist Yarn twist Spinning draft Spindle speed Traveller weight Spacer size.
Spinning technology The spinning technology has a significant role in determining yarn hairiness. Patnaik et al. (2007) compared the hairiness of ring, rotor, air-jet and friction (DREF II) spun yarns produced from 1.5 denier and 44 mm long viscose staple fibres. The hairiness was tested using a Zweigle G566 instrument as well as by a Leica MZ6 microscope. Hairiness values of DREF II yarns were the maximum followed by ring, air-jet and rotor yarns. DREF II yarns had a large number of looped hairs (87.9%) which are created during the sudden deceleration of the fibres at the spinning drums. Moreover, the spinning tension of friction spinning technology is also very low and thus it creates a very loose yarn structure. This leads to more protruding and looped hairs in the case of DREF II yarns. Air-jet yarns showed lower hairiness than ring spun yarns due to the presence of wrapper fibres at regular intervals. In rotor spinning, the fibres are condensed on the collecting groove of the rotor due to high centrifugal forces and the whole assembly is twisted at the same time. Under these conditions, the fibres are better controlled, which leads to extremely low hairiness. The presence of wrapper fibres also reduces the hairiness of rotor spun yarns. However, the proportion of looped hairs is
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also very high in the case of rotor spun yarns (88.9%). This may be due to the buckling of fibres during aerodynamic deposition at the grooves of the rotor. Looped hairs are the major contributors to the hairiness of all the yarns, followed by the protruding hairs. Most of the hairs are smaller hairs (class interval of 0–1 and 1–2 mm) for all types of yarns. Hair length followed an exponential distribution for all types of yarns. Winding operation Winding increases the hairiness of spun yarns mainly due to the abrasion between the running yarn and the machine parts. Generally, a higher winding speed is associated with more increase in the hairiness level. Ring, rotor, airjet and friction spun yarns show a similar level of rise in their S3 hairiness value after the winding operation (Patnaik et al., 2007). However, the longer hairs rise more rapidly for friction spun yarns as they have a very loose structure. On the other hand, air-jet yarns show a drastic rise in the number of short hairs (<1 mm) after winding. This may be ascribed to the opening of some wrapper fibres by rubbing. Blending and mixing parameters Mixing of two or more varieties of cotton is a very common practice in the spinning industries. Although the mixing of longer and finer cotton reduces the hairiness to some extent, the effect is not very pronounced. The reason could be attributed to the preferential migration of shorter and coarser fibres towards the yarn surface. Addition of soft wastes and comber noil in the mixing increases the yarn hairiness due to the increase in the proportion of short fibres. The effect is more marked for comber noil than the soft waste as comber noil is mainly composed of short fibres. Combing operation Combed yarns are invariably less hairy than the equivalent carded yarns. The combing process eliminates the majority of the short fibres from the feed lap. Therefore, the mean length of the fibre improves and the short fibre content reduces drastically, which ultimately results in a reduction in yarn hairiness. However, this reduction in hairiness with the increase in comber noil is less pronounced when the noil level exceeds 12%. Number of drawframe passages An increase in the number of drawframe passages reduces the yarn hairiness. Drawframe increases the orientation of the fibres and also removes the hooks
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present in the card sliver. Therefore, the mean fibre length increases with the number of drawframe passages and thus the yarn hairiness reduces. However, the positive effect on hairiness will diminish with the increase in the number of drawframe passages. Roving fineness and twist Roving fineness plays an important role in determining the hairiness level of spun yarns. For a given yarn fineness, the hairiness shows concomitant reduction with the fineness of the roving. For example, if 30 Ne ring spun yarn is produced from rovings of 0.8 and 1.0 hanks, then the yarn made with 1.0 hank roving will give less hairiness. If the roving is coarser then the fibres tend to form a wider ribbon in the drafting zone and thus incorporation of the edge fibres becomes difficult. This ultimately increases the hairiness. An increase in roving twist reduces the yarn hairiness, as the spreading of the fibres at the nip of the drafting rollers is prevented to some extent. Yarn twist Yarn twist is the most important process parameter for controlling hairiness. As the twist increases, more torque is applied at the yarn forming zone and thus the probability of a fibre being embedded into the main yarn body increases. For a given yarn delivery speed, this can be attained by increasing the spindle speed, the rotor speed, the jet pressure and the friction drum speed in ring, rotor, air-jet and friction spinning technologies, respectively. Spinning draft Research work by Pillay (1964b) has shown that for the same yarn count as the ringframe draft increases, the yarn hairiness also increases. A higher spinning draft requires coarser roving for the same yarn count. Thicker roving gives rise to a high degree of fibre spread between the rollers. As the ribbon of fibres comes forward, the fibres at the edges of the wider ribbon become hairs. Spindle speed An increase in spindle speed, at constant twist per unit length of yarn, also increases yarn hairiness due to the higher centrifugal forces associated with the higher spindle speed. The effect was similar when the spinning tension was kept constant by reducing the traveller weight with increasing spindle speed.
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Traveller weight In general, a higher traveller weight reduces yarn hairiness. With a higher traveller weight, more twist flows to the spinning zone from the balloon zone and thus the hairiness is reduced. Moreover, a higher traveller weight leads to a higher spinning tension and better binding of the fibres in the yarn body. Spacer size Thicker spacers generally lead to lower hairiness. Spinners generally prefer the thinnest possible spacer with the aim of minimizing the mass unevenness and imperfections in the yarn. However, the use of a thinner spacer can ultimately lead to a significant increase in hairiness. As the size of the spacer is reduced, the gap between the top and bottom apron in the main drafting zone of the ringframe reduces. Thus the fibre strand tends to be flatter and wider, resulting in increased hairiness.
4.3
Yarn hairiness measurement
The basic principles of yarn hairiness measurement could be classified under the following two heads: ∑
Counting the number of fibres longer than a given reference length or longer than a set of reference lengths that are protruding from the yarn body per unit length of yarn. ∑ Measuring the cumulative length of all protruding fibres outside the yarn body per unit length of yarn.
4.3.1 Shirley yarn hairiness tester The Shirley yarn hairiness tester measures yarn hairiness based on an optical principle. The yarn under test is passed between a beam of light rays and the receptor photocell at a constant speed. When a hair passes between the light rays and the receptor, the light rays are momentarily interrupted and an electronic circuit counts the interruption as one hair. The instrument has two sets of yarn guides as shown in Fig. 4.1 (Saville, 1999). The lower set leads the yarn over a guide at a fixed distance of 3 mm from the receptor. The upper set leads the yarn over a movable guide which can be adjusted at a distance of between 1 mm and 10 mm from the receptor. Therefore, testing of hair length can be customized up to a length of 10 mm. The number of hairs counted over a length of 1000 m is reported.
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Alternative yarn path Aperture
Variable 3 mm Fixed 3 mm yarn path
4.1 Shirley yarn hairiness tester (Saville, 1999).
4.3.2 Zweigle yarn hairiness tester This instrument tests the yarn hairiness exhaustively by counting the hairs in 12 different length groups and therefore the distribution of hair in different length groups can be obtained. The hairs are counted simultaneously by a set of photocells arranged at distances of 1, 2, 3, 4, 6, 8, 10, 12, 15, 18, 21 and 25 mm from the yarn. The principle of the instrument is quite similar to that of the Shirley hairiness tester. The yarn and the protruding fibres interrupt the incident light beam and thus cause a variation in the luminance of the light beam. This luminance is recorded by the phototransistor, converted to an electric current and then amplified. The instrument measures the total number of hairs in each length category for the set test length. The instrument also computes the total number of hairs above 3 mm in length, which can be used as a comparison with the results obtained from the Shirley instrument (S3). It also computes a hairiness index, using a rather complicated mathematical expression, which is a non-dimensional numerical value and provides a relative reference to the hairiness level of the yarn.
4.3.3 Uster yarn hairiness tester The hairiness measuring principle of the Uster Tester (III or IV) is different from that of the Shirley and Zweigle instruments, and therefore a direct comparison cannot be made between the results obtained from these instruments. In this instrument the yarn is illuminated by a parallel beam
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of infrared light as it runs through the measuring head. Only the light that is scattered by protruding hairs reaches the detector, as shown in Fig. 4.2 (Saville, 1999). The direct light is prevented from reaching the detector by an opaque stop. The amount of scattered light is converted to an electrical signal and considered as a measure of hairiness. The instrument is thus monitoring only total hairiness, but the Uster evenness data collection system can monitor changes in hairiness along the yarn by means of a diagram, spectrogram and CV of hairiness in a manner similar to that used in evenness testing.
4.3.4 Comparison of hairiness results from different instruments As the three instruments described above express the yarn hairiness in different forms, comparing the results without proper understanding often becomes misleading. Some researchers have attempted to derive the relationship between the results obtained from these instruments. Barella and Manich (1988) reported that the correlation between the S3 values obtained from the Shirley and the Zweigle G 565 was 0.73. Basu (1999) developed the following empirical relation between the hairiness results (number of protruding fibres longer than 3 mm) obtained from the Shirley and Zweigle G 565 instruments:
HZweigle = 0.573HShirley + 247.54 (correlation coefficient = 0.98)
Basu also used a simple expression to calculate the K value from the results of the Zweigle G 565 tester. This K value could be compared directly with the hairiness index measured by the Uster Tester III.
K=
11
1 ∑ N L + N12 L12 100 ,000 i=1 i i Yarn Scattered light
Receiver
Transmitter Stop
Direct light
4.2 Uster yarn hairiness tester (Saville, 1999).
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where
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li + li +1 2 li = length of hairs (mm) in class i li+1 = length of hairs (mm) in class (i +1) Ni = number of hairs in class i per 100 m length of yarn. Li =
He found that the K value was lower than the hairiness index (H) value given by the Uster Tester III, because hairs smaller than 1 mm in length were not considered in the above expression for K. The correlation coefficient between the Uster Tester hairiness index value and the Zweigle K value, calculated by the above equation, was found to be encouraging (0.83). The relationship between the results reported by different instruments is shown in Fig. 4.3.
4.3.5 Effect of testing parameters on yarn hairiness The speed of yarn traverse during hairiness testing often influences the hairiness results (Wang, 1998a). The hairiness could be measured at a speed as high as 400 m/min. Therefore, high air drag forces act on the protruding fibres. In ring spun yarns, most of the hairs are trailing. Therefore, while unwinding from the ringframe package, these hairs become leading and, due to the air drag, the projected length of the fibres tends to increase. However, for longer hairs the effect may become just the opposite (especially at high 80
10
8
Zweigle K¢
SDL Hairs/1000 m ¥ 103
60
40
6
4
20 2 r = 0.98 0 0
5 10 15 20 25 30 35 40 45 50 Zweigle S3/1000 m ¥ 103
r = 0.83 0 0
2
4 6 Uster UT3 H
8
10
4.3 Correlation of yarn hairiness results from different instruments (Basu, 1999).
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traverse speed) as the longer hairs may bend as a result of a higher bending moment acting at their bases. This may ultimately result in reduction in the number of hairs in the long length group. The experimental results obtained by Wang (1997, 1998b) ratified the above mechanisms, although there were also a few contradictions (Wang and Chang, 1999). The S3 values of rotor spun (18 tex) yarns measured by the Zweigle G 565 tester at different speeds are depicted in Fig. 4.4. Wang et al. (1999) also studied the effect of testing speed (Uster Tester III) on the hairiness of worsted yarns spun with different levels of twists. Irrespective of yarn twist level, hairiness measured at a speed of 400 m/min was higher than that measured at 100 m/min or 25 m/min, as shown in Fig. 4.5. The hairiness value increases slightly when the testing speed is increased from 25 m/min to 100 m/min. However, this was not statistically significant at a 5% level.
S3 value (hairs/m)
30
20
10
0
10
20
30
40 50 60 70 Test speed (m/min)
80
90
100 110
4.4 Effect of test speed on the hairiness of 18 tex rotor yarns (Wang, 1998b).
Average hairiness index
8 7.5 7 6.5
373 tpm
6
563 tpm
5.5
665 tpm
5 4.5 4 25
100 400 Test speed (m/min)
4.5 Effect of test speed on the hairiness of worsted yarns (Wang et al. 1999).
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4.4
Importance of yarn hairiness
4.4.1 Effect of yarn hairiness in spinning The effect of yarn hairiness on air drag, tension and power consumption in ring spinning has been researched by Tang et al. (2004a,b, 2006) and Chang et al. (2003). Researches by Tang et al. (2006) showed that yarn hairiness has a considerable influence on air drag in ring spinning. Theoretically the power (P) required to overcome skin friction drag on the surface of a revolving yarn package is expressed as follows:
P = 1 r(πDV )3 ACd 2
where r is the density of the air, D is the package diameter, V is the revolutions per second for the package, A is the surface area of the package and Cd is the skin friction coefficient on the yarn package surface. The experimental results showed that the effect of yarn hairiness on the skin friction coefficient is inversely proportional to the spindle speed. At a low spindle speed of 2000 rpm, the skin friction coefficient was 98% higher for a normal package as compared to the package of singed yarns. However, at a spindle speed of 16,000 rpm, the skin friction coefficient was only 16% higher for the normal package as compared to the package of singed yarns. On average, 25% of the air drag on the surface of a rotating cotton package is contributed by the hairiness, whereas it is around 35% for the wool yarn package. The difference between the normal and singed yarn packages in terms of air drag is higher at low spindle speeds and diminishes as the spindle speed in rpm is increased. The air drag on the ballooning cotton yarn during rotation reduces by around 9% after singing. It is expected that a ringframe package will require more power for rotation if the yarn is hairy. Chang et al. (2003) studied the effect of yarn hairiness on power consumption in rotating a ring spun yarn package and concluded that the effect of hairiness on power consumption is statistically significant at a 5% level. The theoretical model developed by them showed that the power requirement to rotate a package during ring spinning will depend on factors like the number of hairs, hair length, spindle speed and package size. Practical experiments also showed that power consumption in ring spinning increases with the increase in the number of hairs and hair length.
4.4.2 Effect of yarn hairiness in weaving and knitting Weaving In the case of shuttle looms, hairiness of yarns can prevent the formation of clear shed which is essential for the passage of the shuttle. During the
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shedding operation, a yarn may become entangled with its neighbour due to repeated abrasion. This may also lead to warp breakage. Therefore, size coatings are applied on the surface of the yarns so that all the protruding hairs are laid down on the yarn body and a clear shed is formed for the passage of the shuttle or other weft carriers. The size uptake is directly related to the level of yarn hairiness. Therefore, the sizing operation becomes more expensive for hairy yarns. The yarn hairiness influences the velocity profile of the yarn during weft insertion in the air-jet weaving system. The air-drag force acting on the yarn is expressed by the following equation: Drag force (D ) = 1 rCf A(Vrel )2 2
where r is the density of the fluid (air), Cf is the drag coefficient, A is the surface area of the yarn and Vrel is the relative velocity between air and the weft. The drag coefficient is expected to be higher for a hairy yarn and therefore the acceleration and velocity of the hairy weft will be higher. Adanur and Turel (2004) experimentally verified the effect of yarn hairiness on the weft velocity profile in the air-jet weaving system (Fig. 4.6). They found that both the initial acceleration and the yarn velocity across the loom were significantly higher for the yarn with an S3 value of 4293 than for the equivalent yarn with an S3 value of 903. Knitting As the production speed of knitting machinery increases, fluff generation becomes a major cause of serious process problems in the case of cotton yarns. All contact points of the yarn on the circular knitting machine are
Yarn velocity (m/s)
40
S3 = 4293 S3 = 903
35 30 25 20
31.5
63
94.5 126 157.5 Distance (cm)
189
220.5
4.6 Effect of hairiness on the velocity profile of the weft in air-jet weaving (Adanur and Turel, 2004).
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potential places for fluff shedding. The problem becomes more serious when processing yarns having high hair severity (long hairs) rather than high overall hairiness. Besides, to achieve the required knitted fabric properties, short hairs are desirable whereas long hairs are problematic as they cause end-breaks and create a fuzzy appearance and pilling. Knitting defects are sometimes identified during the knitting process while others appear after dyeing and finishing. Yarn hairiness can cause a ‘Barre’ effect in fabrics (Srinivasan and Balamurugan, 2008). This shows up more prominently after dyeing and affects the appearance of the finished fabric. Knitting yarns are generally waxed, which not only reduces the friction between the yarn and the machine parts but also lays the protruding fibres on the yarn body and thereby reduces the chances of fluff generation.
4.4.3 Effect of yarn hairiness on fabric properties Pilling The hairiness of yarns influences the pilling tendency of the fabric. During abrasion, the hairs entangle with each other and thus create pills which spoil the appearance of the fabric. This is more dangerous for synthetic yarns as the strength of the synthetic fibre is high and thus the pills do not fall away easily. Research work conducted by Beltran et al. (2007) on single jersey knitted wool fabrics has shown that a relatively high reduction in hairiness is required to make significant improvements in fabric pilling. They compared three technologies, namely conventional ring spinning, Solospun and JetWind, and found that the yarn hairiness was 46% lower for Solospun and 33% lower for JetWind with respect to the ring yarns. Interestingly, they found that the final fabric made from JetWind yarn had one grade better pilling rating than fabric made from ring yarns, whereas fabric made from Solospun yarn had only a half grade improvement over fabric made from ring yarns. The improved pilling performance observed with the JetWind method over the Solospun indicates that the number of hairs is not the singular aspect that influences fabric pilling. The hairiness configuration and associated fibre security within the yarn or fabric structure also play major roles. However, Lohrasbi et al. (2003) found that for yarns made from blends of shrinkable and non-shrinkable acrylic fibres, the correlation between yarn hairiness and fabric pilling is not very strong. They found that the most hairy yarn is actually producing the minimum number of hairs in the knitted fabric. Abrasion resistance The abrasion resistance of the fabric also deteriorates with increase in yarn hairiness. Akaydin (2009) found that the abrasion resistance of single jersey,
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rib and interlock knitted fabrics made from compact yarns was better than for the equivalent ring spun yarns. They opined that the lower hairiness of compact yarn is one of the main reasons for improved abrasion resistance. Thermal properties Yarn hairiness can significantly influence thermal comfort properties of fabrics. Generally yarns with higher hairiness demonstrate lower thermal conductivity and higher thermal resistance as the protruding hairs can trap the static air, which is a bad conductor of heat. Therefore, fabrics made from low twist yarns give lower thermal conductivity and higher thermal resistance than fabrics made from high twist yarns. Similarly, fabrics made from carded yarns show lower thermal conductivity and higher thermal resistance than fabrics made from equivalent combed yarns. Ozdil et al. (2007) found that the thermal absorptivity value increases (cooler feeling) with an increase in yarn twist. This is explained by the lower hairiness of the high twist yarns. A decrease in hairiness increases the contact surface area between the fabric and the skin and thus creates a cooler feeling.
4.5
Modelling of yarn hairiness
4.5.1 Mathematical and statistical models Modelling of yarn properties is one of the most fascinating areas of textile research, and several researchers (Chasmawala et al., 1990; Majumdar and Majumdar, 2003; Neckar and Voborova, 2003; Baykal et al., 2007) have attempted to develop mathematical and statistical models to predict the hairiness of spun yarns using the fibre properties, blend proportion, process parameters and yarn count as inputs. Majumdar and Majumdar (2003) developed the following multiple linear regression equation to predict ring spun yarn hairiness (Uster Tester III) from the cotton fibre properties:
Hairiness = 23.36 – (0.019 ¥ bundle tenacity)
– (0.242 ¥ fibre elongation) – (0.194 ¥ UHML)
– (0.112 ¥ UI) – (0.288 ¥ micronaire)
– (0.028 ¥ Rd) – 0.143(+ b) – (0.084 ¥ yarn count)
where UHML is upper half mean length, UI is uniformity index, Rd is the reflectance degree and + b is the yellowness value of cotton fibre. The correlation coefficient between the actual and predicted hairiness, using the above equation, was around 0.93. The negative coefficient of micronaire is rather surprising as higher cotton fibre micronaire is expected to increase the yarn hairiness. However, this may have happened due to the
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inherent correlation between the properties of cotton fibres. Chasmawala et al. (1990) derived the following regression equation for predicting the hairiness of air-jet spun yarns expressed by the number of hairs per eight yards:
Hairiness = 4561 – (42.8 ¥ number of wild wrapper fibres)
– (92.4 ¥ number of wild fibres)
– (35.1 ¥ number of core fibres)
4.5.2 Artificial neural network modelling of yarn hairiness: a case study In the last two decades intelligent models such as artificial neural network (ANN) and neuro-fuzzy systems have been used for the modelling and prediction of yarn properties. These models are fault tolerant and have a very high prediction accuracy. ANN is a potent data-modelling tool that is able to capture and represent any kind of input–output relationships. The motivation for development of ANN stemmed from the desire to develop an artificial system that can perform intelligent tasks similar to those performed by the human brain. A typical multi-layer ANN is shown in Fig. 4.7. Here, one or more hidden layers can be sandwiched between the input and output layers. The number of hidden layers and the number of neurons per layer vary depending on the complexity of the problem. Each neuron receives a signal from the neurons of the previous layer and these signals are multiplied by separate synaptic weights (W). The weighted inputs are then summed up and passed through a transfer function (usually a sigmoid), which converts the output to a fixed range of values. The output of the transfer function is then transmitted to the neurons of the next layer. Finally the output is produced at the neurons of the output layer and the error signal (the difference between the actual and predicted values) is calculated. The error signal is then used to optimize the connection weights between the neurons of different layers using suitable algorithms. WK1 X1
WKn Output
Inputs Xn
Hidden layer
4.7 A simple artificial neural network model.
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In this case study (Majumdar and Majumdar, 2003) of yarn hairiness prediction, cotton crop study data of 1997 and 1998 from the International Textile Centre, Texas, USA, were used. Cotton fibre and yarn data of 87 and 108 samples for ring and rotor spun yarns, respectively, were used for modelling. Seven cotton fibre properties measured by HVI, namely fibre bundle tenacity, elongation, upper half mean length (UHML), uniformity index (UI), micronaire, reflectance degree and yellowness were used as inputs to the ANN model. Yarn count (Ne) was also introduced in the model as an input. The only output from the ANN model was the hairiness index as measured by the Uster Tester III. For the training of ANN, 72 and 88 sets of input–output data were used for ring and rotor spun yarns, respectively. The remaining data sets (15 for ring spun yarns and 20 for rotor spun yarns) were used for the validation of trained networks. ANN models having only one hidden layer were used. However, the number of neurons in the hidden layer was varied from six to 14 with an increment of two at each step. To overcome the problem of an undertrained or overtrained network, training ceased as soon as the mean squared error (MSE) in the test set data reached the minimum level. Training was done with a back-propagation algorithm. The log-sigmoid transfer function was used in the hidden and output neurons. Prediction performance of the ANN model After the completion of training, the test set data were presented to the trained network for the prediction of yarn hairiness. Statistical parameters such as the correlation coefficient (R) between the actual and predicted values, the mean absolute error percentage and the mean squared error (MSE) were calculated to appraise the predictive power of ANN and to compare it with that of regression models developed using the same data (Table 4.1). It was observed that the ANN model showed a very high prediction accuracy (R > 0.95) for ring and rotor yarn hairiness. The mean error of prediction was lower than 3% for ring spun yarn and 2% for rotor spun yarn. Detailed analysis of the ANN model revealed that for ring spun yarns, three prediction results Table 4.1 Prediction performance of ANN and regression models Yarn type
Statistical parameter
Prediction models
ANN
Linear regression
Ring
Correlation coefficient Mean absolute error % Mean squared error
0.958 2.75 0.039
0.929 3.99 0.066
Rotor
Correlation coefficient Mean absolute error % Mean squared error
0.952 1.75 0.0076
0.934 2.07 0.011
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out of 15 test set data exhibited more than 5% absolute error. In contrast, out of 20 test set data, there were no such prediction results for rotor spun yarns. This demonstrates that the prediction performance was more accurate and consistent for rotor spun yarns. In comparing the results of the ANN and regression models, it was observed that the mean absolute error percentage of prediction is higher and the correlation coefficient is lower for the regression model (Table 4.1). This strengthens the perception that some non-linear relationship exists between fibre properties and yarn hairiness, which cannot be captured by the linear regression model (Zhu and Ethridge, 1997). The ANN model having only one hidden layer is capable of handling non-linear relationships. Therefore, the prediction accuracy of ANN models is better than that of the linear regression model. Figure 4.8 depicts the absolute error percentage of prediction in individual test samples of ring spun yarns by the ANN and regression models. Out of these 15 test set samples, ANN shows a lower error of prediction than the regression model in 11 samples.
4.6
Yarn hairiness reduction
4.6.1 Compact spinning technology The compact spinning system, which is a development of the ring spinning system (Cheng and Yu, 2003; Basel and Oxenham, 2006; Celik and Kadoglu, 2004; Nikolic et al., 2003) , was first demonstrated at ITMA 99. In conventional ring spinning, the width of the fibre flowing ribbon at the 10
ANN Regression
Absolute prediction error %
9 8 7 6 5 4 3 2 1 0 1
2
3
4
5
6
7 8 9 10 11 Sample number
12 13
14 15
4.8 Prediction performance of ANN and regression model for ring spun yarns.
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back of the front roller nip is higher than the width of the spinning triangle. Therefore, some of the fibres, due to their bending rigidity, fail to incorporate themselves into the main yarn body, causing hairiness. In compact spinning, the width of the fibre flowing ribbon is reduced and becomes equal to that of the spinning triangle. Therefore, most of the fibres are incorporated in the yarn body and consequently the hairiness is reduced. Rieter, Zinser and Suessen are the major manufacturers of compact spinning machines. In the Rieter compact spinning machine (K44), the front bottom roller has a larger diameter and is perforated to aid the air suction. The slot, which facilitates the air suction, extends between the nip created by the front top roller and the nip roller (Fig. 4.9). Therefore the width of the fibre ribbon is reduced significantly (from B to b) between the two nips. Cheng and Yu (2003) compared the properties of compact yarns spun on Rieter ComforSpin K 40 machines and those of conventional ring spun yarns. They found that the hairiness of the compact yarns was much lower than that of the ring spun yarns. However, the advantages of compact spun yarns were found to diminish as the yarn count became coarser, as shown in Fig. 4.10. The aerodynamic condensing system of compact spinning technology has better fibre control for fine counts where there are fewer fibres in the ribbon. When the yarn becomes coarser the effectiveness of the compacting action reduces. Moreover, in case of coarser yarns, the slots on the stationary drum of the condensing system could be blocked more frequently by the shorter fibres through the holes of the perforated drum. Basel and Oxenham (2006) spun 100% Pima cotton and 50:50 cotton:polyester blended yarns at different twist multipliers (2.8, 3.2, 3.6, 4.0 and 4.4) using Suessen Elite® and conventional ring spinning machines. They found that the hairiness of the compact spun yarn is significantly lower than that of ring spun yarns. However, the difference in hairiness level diminished as the twist multiplier increased, as shown in Fig. 4.11. It could therefore be inferred that the superiority of compact spinning technology
B
B
b
(a)
b
(b)
4.9 Spinning triangles in (a) ring spinning and (b) compact spinning (source: technical literature of Rieter Spinning Systems).
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Mean hairiness
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5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0
COM4 Ring
Ne 38
Ne 50 Ne 60 Yarn count
Ne 80
4.10 Hairiness of compact and ring spun yarns in different counts (Cheng and Yu, 2003). 7
Conventional Compact
6
Hairiness
5 4 3 2 1 0
2.8
3.2
3.6 Twist multiplier
4
4.4
4.11 Hairiness of compact and ring spun yarns in different twist levels (Basel and Oxenham, 2006).
over ring spinning technology is more marked for finer yarns and for low twist levels. Application of compact spinning technology to long staple yarns has also been investigated by Celik and Kadoglu (2004). They used a compact spinning attachment (Suessen Elite®) for converting the ring spinning unit. Normal ring and compact yarns of 19 tex and 25 tex were spun from 100% wool, 45:55 wool:polyester, 50:50 wool:acrylic and 100% acrylic fibres using twist factors ranging from 2530 to 3160. For all the materials and twist levels, the compact spun yarns demonstrated significantly lower hairiness as measured by the Uster Tester III and the Zweigle G 565 tester. The Zweigle hairiness results further showed that the occurrence of hairs in the longer length class was much lower in the case of compact spun yarns. In the case of long staple spinning also, the benefit of compact spinning is more visible at lower levels of yarn twist.
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4.6.2 Jet-ring spinning system Jet-ring spinning technology (Fig. 4.12) amalgamates the ring spinning and air-jet spinning technologies primarily with the objective of reducing yarn hairiness (Wang, 1999; Cheng and Li, 2002; Wang et al., 1997). In jetring, an air-jet is positioned between the lappet (pigtail) guide and the front roller nip of the ring spinning machine. The air-jet creates upward swirling of air against the direction of movement of the yarn. Thus it precludes the possibility of increasing the hairiness of the yarn, as in ring spinning mostly trailing hairs are generated. The swirling air current twists the yarn in the opposite direction to the main twist which is applied by the ring and traveller assembly. Therefore, over the air-jet the yarn first gets untwisted and then gets twisted again. This loosening and tightening of the structure facilitates the incorporation of some of the protruding fibres in the main yarn body. Yarn piecing is also simple in the jet-ring spinning system. However, for the best performance of the system, parameters such as air pressure and the distance between the front roller nip and the air-jet must be optimized. Besides the design parameters of the jet such as the angle of the jet orifice, the diameter of the twisting chamber and the length of the nozzle play important roles in the wrapping action of the protruding fibres. Cheng and Li (2002) investigated the effect of spindle speed, air pressure, twist factor and the distance between the front roller nip and the nozzle inlet on the hairiness of cotton and polyester jet-ring spun yarns. Air pressure and yarn hairiness were negatively correlated, as expected. The hairiness reduction was more pronounced in the case of cotton yarns as compared to polyester yarns as shown in Fig. 4.13. The distance between the front roller nip and the nozzle inlet has the minimum influence on yarn hairiness. However, this
Front rollers
Air jet
Pigtail guide
Ring and traveller
Yarn bobbin
4.12 Jet-ring spinning system (Wang, 1999).
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Number of hairs > 3 mm
120 100 80 60 40 Cotton jet-ring
20
Polyester jet-ring
0 0
0.5
1 1.5 Pressure (bar)
2
2.5
4.13 Effect of air pressure on yarn hairiness in jet-ring spinning (Cheng and Li, 2002).
distance is very important for trouble-free running of the system, because any disturbance created by the air-jet can reach the spinning triangle and cause a yarn break if the distance between the front roller nip and the nozzle inlet is very small.
4.6.3 Jet-winding or nozzle winding system In the jet-winding or nozzle-winding system an air-jet is used in the winding machine to reduce the yarn hairiness (Rengasamy et al., 2005, 2006; Patnaik et al., 2006, 2008; Zeng and Yu, 2004; Wang and Miao, 1997; Chellamani et al., 2000). This approach seems to be attractive as winding generally increases the hairiness due to the abrasion of the yarn with various machine parts. The nozzle-winding technique (Fig. 4.14) was used by Patnaik et al. (2007) to reduce hairiness of ring, rotor, air-jet and DREF-II yarns spun from the same viscose staple fibres (1.5 denier and 44 mm length). Yarns were passed through an air-nozzle with air inlets having an axial angle of 45° and a yarn channel diameter of 2.2 mm. The air pressure in the nozzle was kept at 0.9 bar and the airflow in the nozzle was along the yarn movement. S3 values for nozzle-wound yarns were found to be nearly 17–30% less than that of the corresponding spun yarns. However, in comparison with the yarns wound without a nozzle, the nozzle-wound yarns had 20–37% lower S3 values. The maximum reduction in S3 values, with respect to the parent spun yarns, was found for DREF-II yarns (30%) followed by ring spun (28%), air-jet (20%) and rotor spun yarns (17%). The greater the number of hairs present on a yarn, the higher is the hairiness reduction by the nozzle. It was observed that the number of hairs from all the hair length groups is invariably reduced by the nozzle winding system. However, the reduction is larger for longer hairs than for shorter ones, because more air-drag forces act on the longer hairs.
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Winding drum Tension sensor Knotter Electronic clearer Tensioner Nozzle housing
Ring yarn
4.14 Jet-winding system (Patnaik et al., 2008).
Besides, after bending, the long hairs are tied up with the yarn body by the protruding hairs in their vicinity as they are wrapped by the action of air drag forces. The percentage reduction in the number of short looped hairs is much lower than for the longer looped hairs, indicating the high resiliency of the former and the associated difficulty in tying them with the yarn body. Significant amounts of research (Rengasamy et al., 2005, 2006; Patnaik et al., 2006, 2008; Zeng and Yu, 2004) have been conducted in recent years to optimize the parameters of the jet-winding process such as the axial angle of the jet, jet diameter, air pressure and winding speed. Techniques such as design of experiments (Box and Behnken), numerical simulation and computational fluid dynamics (CFD) have been used to analyse the air–fibre interaction during the jet-winding process. Rengasamy et al. (2005) tried to optimize the process conditions of the jet-winding system using the Box and Behnken factorial design approach and computational fluid dynamics (CFD) for cotton ring spun yarns. Two sets of experiments were conducted for optimizing the jet angle and jet diameter. In the first set of experiments, three jet angles (40°, 45° and 50°) were used, keeping the jet diameter constant at 2.2 mm. In the second set of experiments, the jet angle was kept constant at 40° and the jet diameter was varied (1.8 mm, 2.2 mm and 2.6 mm). The other two variables for both sets of experiments were yarn linear density (10, 20 and 30 tex) and winding speed (800, 1000 and 1200 m/min). It was observed that 45° of jet angle was optimum, followed by the 40° jet angle. Analysis by CFD modelling revealed that the higher axial velocity in the jet at 45° (91 m/s),
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in comparison to the jet at 40° (84 m/s), increases the swirling intensity, causing more wrapping of fibres around the yarn body which thus leads to more reduction in yarn hairiness. The jet diameter of 2.2 mm was found to be the best from the hairiness reduction point of view. In a similar study on polyester yarns (30 tex) Patnaik et al. (2008) studied the effect of air channel diameter, jet angle, fibre fineness and air pressure on the S3 hairiness reduction. They conducted two separate experiments with three factors and three levels. The three fibre deniers were 1, 1.2 and 1.4 and the air pressure was 0.5, 0.7 and 0.9 bar. In one experiment, only the axial angle of the air inlets was varied from 40° to 50°, keeping the jet diameter constant at 2.2 mm. In the second setup, the jet diameter was varied from 1.8 mm to 2.6 mm keeping the axial angle of the air inlets constant at 40°. It was found that when the jet angle and jet diameter are kept constant, a higher air pressure (0.9 bar) and a high fibre denier (1.4) give the maximum reduction in S3 hairiness value as shown in Fig. 4.15. The air drag acting on the fibre is proportional to the square root of the denier, and the bending rigidity of the fibre is proportional to the square of the denier. Therefore, theoretically, it is expected that higher denier polyester fibres will show less reduction in hairiness. However, the statistical effect of presentation of more hairs to the nozzle by the coarser fibre yarn seems to be playing a predominant role in hairiness reduction. Patnaik et al. also reported that for constant fibre denier and jet diameter, a combination of higher air pressure (0.9 bar) and 45° of jet angle gives the best performance (Fig. 4.15). CFD modelling also ratified the above results. The resultant velocity of the air acting on the yarn surface and on hairs (near the wall of the jet) is higher in the case of the nozzle with 45° axial angle in comparison to the nozzles with 40° and 50° axial angles. While experimenting with different jet diameters, the maximum air velocity was observed in the vicinity of the nozzle with 1.0
1.0
28
23 22
20 0.0
–1.0 –1.0
17
16
1.0
14
19 16 15
–0.5
10
15
–0.5 0.0 0.5 Fibre fineness (a)
20
18
16
14
12
10 –1.0 –1.0
21
17
22
–0.5
Air pressure
0.0
24
Air pressure
0.5
26
0.5
–0.5 0.0 0.5 Axial angle of air inlets (b)
1.0
4.15 Effect of jet-winding parameters on hairiness reduction (Patnaik et al., 2008).
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1.8 mm diameter followed by those of 2.2 and 2.6 mm diameter. However, in terms of hairiness reduction, the jet of 2.2 mm diameter was the best, followed by nozzles with 1.8 mm and 2.6 mm diameters. For the nozzle with the smaller diameter (1.8 mm), the air velocity was very high and the diffusing tendency of the air velocity was less. Therefore rubbing of the yarn at the wall of the nozzle might have affected the hairiness reduction.
4.6.4 Modified yarn path in ring spinning The spinning triangle produced during ring spinning is not symmetrical. If the yarn is twisted in the Z direction then the fibres on the right-hand side of the spinning triangle often undergo a pre-twisting process. In contrast the fibres on the left-hand side of the triangle are under a lower level of control and are therefore, more prone to hair formation. However, this problem could be mitigated by using two approaches to the modified yarn path in ring spinning (Fig. 4.16). In the case of the left diagonal approach (Fig. 4.16(a)), the yarn delivered from a drafting unit is taken up by the adjacent bobbin to the left of the drafting unit, instead of the bobbin directly under the drafting unit. This arrangement will ensure better control of the fibres situated on the left-hand side of the spinning triangle as compared to the conventional arrangement. The fibres on the right-hand side of the spinning triangle will still remain under the pre-twisting control, whereas the fibres on the left-hand side of the triangle are better twisted due to the reduction of distance. The experimental results show that with the left diagonal arrangement (Fig. 4.16(a)) the hairiness in the yarn reduces, whereas it increases with the right diagonal arrangement (Fig. 4.16(b)). Wang and Chang (2003) conducted practical experiments with the 24 spindle Cognetex FLC worsted ring frame for the verification of the above hypothesis. However, the left diagonal approach for the Z twisted yarns increased the yarn hairiness, but in the case of the right diagonal approach, yarn hairiness reduced. The number of S3 hairs is produced by a different arrangement as shown in Table 4.2. The right diagonal yarn path results in fewer hairs in almost all the length groups, and the reduction in the average S3 value was about 8.3% in comparison with the average S3 value for the conventional ring spun yarns. This yarn hairiness reduction may be due to the increased pre-twisting effect on the right-hand side of the spinning triangle when the right-diagonal yarn path is used. Pre-twisting of fibres occurs primarily on the right-hand side of the twist triangle. With the right diagonal arrangement, there is an increased concentration of fibres on the right-hand side of the skewed triangle, so an increased number of fibres will be pre-twisted. This pre-twisting improves the control of fibres and allows more fibres to be incorporated into the bulk of the yarn structure, thus
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Technical textile yarns Delivery roller
Traveller
Ring
Bobbin Position 2 Position 1
Spindle drive
(a) Delivery roller
Traveller Ring
Bobbin Position 2 Position 1 (b)
Spindle drive
4.16 (a) Left and (b) right diagonal arrangements (Wang, 1999).
reducing hairiness. Besides, the lack of fibre control on the left-hand side of the triangle may lead to more fly generation from that side. As a result the hairiness is reduced.
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Table 4.2 Average S3 values per 100 m length of yarn Spinning arrangement
Average S3 value
Conventional Right diagonal Left diagonal
2333 2084 2658
Source: Wang et al., 1999.
4.7
Conclusions
Yarn hairiness is a very complex characteristic as it is influenced by the fibre properties, process parameters and testing conditions. A lot of research work has been conducted to understand the mechanism of hair formation during the spinning and winding processes and to develop methods to counter such formation. Apart from influencing the efficiency of the weaving and knitting processes, hairiness also influences the tension and power consumption during ring spinning, which has long been ignored by spinning technologists. On the other hand, the production of absolutely hair-free yarns may have an adverse effect on fabric comfort and handle characteristics. Therefore, it is of paramount importance to have systems that are able to control and engineer the hairiness level in a spun yarn. In the last two decades, compact spinning technology has emerged as a very popular method for reducing yarn hairiness, but the cost of yarn production has also gone up significantly. Systems such as jet-ring and jet-wind have also been used to reduce hairiness in spinning and winding machines. It is envisaged that more research will be initiated in the near future to develop cost-effective systems for the reduction of yarn hairiness.
4.8
Acknowledgement
The author is thankful to Journal of the Textile Institute (Taylor & Francis), Textile Research Journal (Sage Publications Ltd.), Research Journal of Textile and Apparel and Indian Journal of Fibre and Textile Research for giving permission to reproduce some of the figures.
4.9
References
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Atlas, S., and Kadoglu, H., 2006, ‘Determining fibre properties and linear density effect on cotton yarn hairiness in ring spinning’, Fibres and Textiles in Eastern Europe, 14(3), 48–51. Barella, A., 1983, ‘Yarn hairiness’, Textile Progress, 13(1), 1–61. Barella, A., 1993, ‘The hairiness of yarns’, Textile Progress, 24(3), 1–49. Barella, A., 1997, ‘Yarn hairiness update’, Textile Progress, 26(4), 1–31. Barella, A., and Manich, A. M., 1988, ‘Influence of spinning process, yarn linear density and fibre properties on hairiness of ring-spun and rotor-spun cotton yarns’, Journal of the Textile Institute, 79(2), 189–197. Basel, G., and Oxenham, W., 2006, ‘Comparison of properties and structures of compact and conventional spun yarns’, Textile Research Journal, 76(7), 567–576. Basu, A., 1999, ‘Assessment of yarn hairiness’, Indian Journal of Fibre and Textile Research, 24, 89–92. Baykal, P. D., Babaarslan, O., and Rizvan, E., 2007, ‘A statistical model for the hairiness of cotton/polyester blended OE rotor yarns’, Fibres and Textiles in Eastern Europe, 15(4), 46–49. Beltran, R., Wang, L., and Wang, X., 2007, ‘A controlled experiment on yarn hairiness and fabric pilling’, Textile Research Journal, 77(3), 179–183. Celik, P., and Kadoglu, H., 2004, ‘A research on the compact spinning for long staple yarns’, Fibres and Textiles in Eastern Europe, 12(4), 27–31. Chang, L., Tang, Z. X., and Wang, X., 2003, ‘The effect of yarn hairiness on energy consumption in rotating a ring-spun yarn package’, Textile Research Journal, 73(11), 949–954. Chasmawala, R. J., Hansen, S. M., and Jayaraman, S., 1990, ‘Structure and properties of air-jet spun yarn’, Textile Research Journal, 60, 61–69. Chellamani, K. P., Chattopadhyay, D., and Kumarasamy, K., 2000, ‘Yarn quality improvement with an air-jet attachment in cone winding’, Indian Journal of Fibre and Textile Research, 25(4), 289–294. Cheng, K. P. S., and Li, C. H. L., 2002, ‘JetRing spinning and its influence on yarn hairiness’, Textile Research Journal, 72(12), 1079–1087. Cheng, K. P. S., and Yu, C., 2003, ‘A study of compact spun yarns’, Textile Research Journal, 73(4), 345–349. Lohrasbi, F., Behzadan, H., and Gharbi, S. H. M. P., 2003, ‘The pilling of acrylic fabrics: effect of fibre moduli’, Research Journal of Textiles and Apparel, 7(2), 26–34. Majumdar, A., and Majumdar, P. K., 2003, ‘Application of artificial neural network for the prediction of yarn hairiness’, in Proceedings of International Conference TEXSCI–2003, Liberec, Czech Republic, 16–18 June, 317–320. Neckar, B., and Voborova, J., 2003, ‘Yarn hairiness: a new theory and experimental method’, in Proceedings of the 7th Asian Textile Conference (CD-ROM), New Delhi. Nikolic, M., Stjepanovic, Z., Lesjak, F., and Stritof, A., 2003, ‘Compact spinning for improved quality of ring spun yarns’, Fibres and Textiles in Eastern Europe, 11(4), 30–35. Ozdil, N., Marmarali, A., and Kretzschmr, D., 2007, ‘Effect of yarn properties on thermal comfort of knitted fabrics’, International Journal of Thermal Sciences, 46, 1318–1322. Patnaik, A., Rengasamy, R. S., Kothari, V. K., and Punekar, H., 2006, ‘Airflow simulation in nozzle for hairiness reduction of ring spun yarns. Part II: Influence of nozzle parameters’, Journal of the Textile Institute, 97(1), 97–101. Patnaik, A., Rengasamy, R. S., Ishtiaque, S. M., and Ghosh, A., 2007, ‘Hairiness of
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spun yarns and their reduction using air-nozzle in winding’, Journal of the Textile Institute, 98(3), 243–249. Patnaik, A., Rengasamy, R. S., Kothari, V. K., and Bhatia, S. K., 2008, ‘Some studies on hairiness reduction of polyester ring spun yarns by using air-nozzles during winding’, Journal of the Textile Institute, 99(1), 17–27. Pillay, K. P. R., 1964a, ‘A study of the hairiness of cotton yarns, Part I: Effect of fibre and yarn factors’, Textile Research Journal, 34(8), 663–674. Pillay, K. P. R., 1964b, ‘A study of the hairiness of cotton yarns, Part II: Effect of processing factors’, Textile Research Journal, 34(9), 783–791. Rengasamy, R. S., Kothari, V. K., Patnaik, A., Ghosh, A., and Punekar, H., 2005, ‘Reducing yarn hairiness in winding by means of jets: Optimisation of jet parameters, yarn linear density and winding speed’, AUTEX Research Journal, 5(3), 127–132. Rengasamy, R. S., Kothari, V. K., Patnaik, A., and Punekar, H., 2006, ‘Airflow simulation in nozzle for hairiness reduction of ring spun yarns. Part I: Influence of airflow direction, nozzle distance, and air pressure’, Journal of the Textile Institute, 97(1), 89–96. Saville, B. P., 1999, Physical testing of textiles, Woodhead Publishing, Cambridge, UK, 104–108. Srinivasan, V., and Balamurugan, S., 2008, ‘Hair severity: An excellent yarn selection tool’, Pakistan Textile Journal, www.ptj.com.pk/2008/03-08/DR.Premier.htm Tang, Z. X., Wang, X., and Fraser, W. B., 2004a, ‘Skin friction coefficient on yarn package surface in ring spinning’, Textile Research Journal, 74(10), 845–850. Tang, Z. X., Wang, X., and Fraser, W. B., 2004b, ‘An experimental investigation of yarn tension in simulated ring spinning’, Fibres and Polymers, 5(4), 275–279. Tang, Z. X., Wang, X., Wang, L., and Fraser, W. B., 2006, ‘The effect of yarn hairiness on air drag in ring spinning’, Textile Research Journal, 76(7), 559–566. Wang, X., 1997, ‘Effect of testing speed on the hairiness of ringspun and sirospun yarns’, Journal of the Textile Institute, 88(2), 99–106. Wang, X., 1998a, ‘Testing the hairiness of a rotor spun yarn on the Zweigle G 565 hairiness meter at different speeds’, Journal of the Textile Institute, 89(2), 167–169. Wang, X., 1998b, ‘Recent research on yarn hairiness testing and reduction, Part I: Hairiness testing’, Research Journal of Textiles and Apparel, 2(1), 13–20. Wang, X., 1999, ‘Recent research on yarn hairiness testing and reduction, Part II: Reduction of yarn hairiness’, Research Journal of Textiles and Apparel, 3(1), 1–8. Wang, X., and Chang., L., 1999, ‘An experimental study of the effect of test speed on yarn hairiness’, Textile Research Journal, 69(1), 25–29. Wang, X., and Chang, L., 2003, ‘Reducing yarn hairiness with a modified yarn path in worsted ring spinning’, Textile Research Journal, 73(4), 327–332. Wang, X., and Miao, M., 1997, ‘Reducing yarn hairiness with an air-jet attachment during winding’, Textile Research Journal, 67(7), 481–485. Wang, X., Miao, M., and How, Y., 1997, ‘Studies of JetRing spinning’, Textile Research Journal, 67(4), 253–258. Wang, X., Huang, W., and Huang, X., 1999, ‘Effect of test speed and twist level on the hairiness of worsted yarns’, Textile Research Journal, 69(12), 889–892. Zeng, Y. C., and Yu, C. W., 2004, ‘Numerical and experimental study on reducing yarn hairiness with the JetRing and JetWind’, Textile Research Journal, 74(3), 222–226. Zhu, R., and Ethridge, M. D., 1997, ‘Predicting hairiness for ring and rotor spun yarns and analyzing the impact of fibre properties’, Textile Research Journal, 67(9), 694–698.
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5
Coatings for technical textile yarns
A. J a l a l U d d i n, Ahsanullah University of Science and Technology, Bangladesh
Abstract: In each application area of technical textiles, advances continue and technical yarn coatings are also in the same queue. The characteristics of a coated yarn depend on the type of polymer used and its formulation, the nature of the textile substrate, and the coating method employed. In this chapter, coating polymers and the additives used in yarn coating are first described. Then the different principles, methods and machinery for yarn coating are discussed. Different uses of coated yarns in terms of industrial, medical, apparel and miscellaneous applications are presented. Remarkably, this chapter introduces some very new coated smart yarns such as antibacterial and antifungal yarns made by plasma technology and very highly conductive biosensing yarns coated by nanomaterials such as carbon nanotubes (CNTs). Key words: coated yarns, metal-coated yarns, plasma-coated yarns, carbon nanotube coated yarns, conductive yarns, smart yarns.
5.1
Introduction
Coating is a covering that is applied to an object. The aim of applying coatings is to improve the surface properties of a bulk material usually referred to as a substrate. A laminate is a material constructed by uniting two or more layers of material together. The process of creating a laminate is lamination, which in common parlance refers to the placing of something between layers of plastic and sealing them with heat and/or pressure, usually with an adhesive. Coating and laminating are involved in many industries including the paper, paint, packaging and textile industries and many more, but the concern of this chapter is textile coating and laminating, especially of yarns. Coating and laminating are mostly textile finishing processes that are designed to enhance and extend the range of functional performance and to add value to a textile and/or to create a textile with specific properties. The uses of these techniques are growing rapidly as the applications for technical textiles become more diverse. Coatings have also facilitated the development of entirely new products and have led to innovations in the area of ‘smart’ materials. Coating and lamination cut across virtually every product group in the textile industry, including composites, where the potential is especially 140 © Woodhead Publishing Limited, 2010
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broad. Coating and laminating are thus increasingly important techniques for adding value to technical textiles. Coatings enable significant cost savings when compared with solid materials of like composition. Cheaper and fragile structures may be coated or laminated to provide higher added value to end-users and higher profit margins to manufacturers. Coatings can be tailored to application-specific requirements quite readily and usually at low cost. Coated textiles are found in defence, transportation, healthcare, architecture, space, sports, environmental pollution control, and many other diverse endproduct uses (see Table 5.1).1 Historically, the earliest recorded use of a coated textile was by the natives of Central and South America, who applied latex to a fabric to render it waterproof. Other materials such as tar, resin and wax emulsions have been used over the years to prepare water-resistant fabrics. Due to their superior properties, rubber and other polymeric materials have become the preferred coatings.2 Section 5.2 of this chapter gives an overview of textile coating and laminating, and Section 5.3 introduces different coating formulations. Section 5.4 describes the chemistry of coating polymers and the technical properties obtained in the substrate by these polymers. The choice of substrates for yarn coating is briefly highlighted in Section 5.5. The possible principles of yarn coating and laminating are discussed in Section 5.6. Section 5.7 depicts the possible methods and machinery for yarn coating. Some useful and novel uses of coated yarns are mentioned in Section 5.8. Future prospects of coated yarns are highlighted in Section 5.9.
5.2
Textile coating and laminating
Textiles are made impermeable to fluids by two processes, coating and laminating. ∑
∑
Coating: Polymer or elastomer, usually in viscous form, is applied directly onto the substrate. The coating must adhere to the textile and a blade or similar aperture controls the thickness of the viscous polymer. The coated material is heated and the polymer is cured (that is, polymerized). Where a thick coating is required this may be built up by applying successive coating layers, layer on layer, so interlayer adhesion must therefore be high. Finally, a thin top layer may be applied for aesthetic or technical enhancement of the coating. Laminating: A pre-made or extruded film is bonded onto the substrate, generally with thermal or adhesive bonding. Curing is generally not required.
Coating and laminating can be used for aesthetics or for function, may be disposable (limited use) or durable. Combinations of polymer and substrate
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Table 5.1 Uses of coated and laminated textiles1 Agriculture Bulk containers Fencing Seed/crop covers Bags Shade materials Irrigation systems Pond liners Irrigation Hoses
Clothing Shoe uppers and linings Artificial leather/bags/belts Rainwear Garment linings Backing/stiffeners Water/stain repellants Combining different materials Gloves Hats Construction Safety fencing Wind covers Concrete curing Safety vests Hoses Conveyer belting Truck covers Drainage ditches Substrate preparation Architectural structures Geotextiles Settling pond liners Irrigation liners Landfill liners and covers Soil stabilizers Erosion barriers Home furnishings Upholstery Trim Carpet backing Drapery backing Bedding Artificial leather Industrial Conveyor belts Filtration Barrier materials Field covers
Abrasive backing Mechanical rubber goods
Medical Barrier materials Implants Bandages Prosthetic devices Gloves Incontinence materials Upholstery Body bags Hygiene products Packaging Bulk containers House wrap Lumber wrap Gas holding Barrier packaging Liquid bulk storage/hauling Waterproof materials Protective Gloves Cut/slash resistant materials Aprons Clean room Chemical/haz-mat suits Footwear Space suits Sport/leisure Athletic shoes Artificial leather/bags/belts Rainwear Backpacks Tents Exercise mats Exercise equipment Balls Seating Field covers Transportation Seating/trim for automotive, trucks, aircraft, buses Hoses/belts Tyres Headlining Seating Carpeting Airbags Truck covers
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are virtually endless. In theory, combinations are chosen for specific properties necessary to ‘do the job’. In practice, combinations are chosen most often because they are available, inexpensive, or simply convenient. Many techniques are used to manufacture a wide range of coated and laminated textiles, such as: ∑ Spread coating – many variants ∑ Dipping/impregnating ∑ Calendering ∑ Hot melt coating/laminating ∑ Film to substrate bonding ∑ Combinations. Broadly, the above-mentioned techniques are spread coating, dip coating, melt coating and lamination. They differ not only in the processing equipment used, but also in the form of polymeric materials used. Thus, paste or solutions are required for spread coating, solutions for dip coatings, and solid polymers such as powders, granules and films for melt coating and lamination. The basic stages involved in these processes include feeding the textile material from rolls under tension to a coating or laminating zone, passing the coated fabric through an oven to volatilize the solvents and cure/gel the coating, cooling the substrate, and subsequently winding it up into rolls. The key to success in textile coating depends upon the type of polymer used and its formulation, the nature of the textile substrate, the coating thickness and weight, the number of layers, the form of the technical textile, the nature of any pre-treatment (such as to stabilize the fabric dimensions prior to coating) and the application of appropriate technology using modern machinery. Machine productivity is important, but flexibility in terms of production speed and the versatility of coating methods are important factors to consider, as well as a high level of process monitoring, process control and automation to satisfy demanding technical specifications. The subject of coated textiles is thus interdisciplinary, requiring knowledge of polymer science, textile technology and chemical engineering. Coating and laminating can involve virtually every textile form: fibres, yarns, fabrics and many polymers/elastomers, rubbers of all types (natural and synthetic), acrylic, vinyl, urethane, silicone, PTFE … the list goes on and on. Traditionally, coating has been applied to woven technical textiles, but increasingly warp-knitted, Rachel, weft-knitted and non-woven fabrics must be coated on the same line. Not only in making traditional textile goods, fibrous materials such as yarns or threads are also used as reinforcing polymeric materials in rigid composites, tyres, conveyor belts, hoses, etc., along with producing smart and intelligent textiles. Very recently yarn surfaces have been coated in a different manner by suitable coating materials to meet
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specific end-uses while retaining their textile character. By coating, yarns can also become ‘multifunctional’.
5.3
Coating formulations for technical textile yarns3
The formulation of a coating is complicated and it can contain a wide range of chemicals depending upon the nature of the polymer, the necessary additives for the specific end-use, whether the coating has to be foamed prior to application, and the type of coating machinery to be used. Coatings may be coloured, translucent or opaque, fluorescent, photo-luminescent or retro-reflective, according to the end-use requirements. Among the many types of chemicals used in coating are: ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑
organic solvents antioxidants surfactants stabilizers for ultraviolet (UV) radiation plasticizers reinforcing fillers activators diluting fillers accelerators pigments vulcanizing agents flame retardants water-repellents.
It is important that the coating formulation is a homogeneous mixture and a variety of high-speed and propeller stirrers are used to achieve this. In some instances homogenizers may be required to break up larger aggregates, especially in thin coating layers. Where the coating mixture has to be foamed, a dynamic foam generator – which has twin rotors rotating within stators – may be used. The intermeshing pins on the rotors and stators and the supply of air/gas cause the formation of a large number of microbubbles. Consequently, a cellular coating layer is formed, usually of the microporous type, if the foamed coating is cured before the bubbles can collapse. High-solids coatings generate heat through friction in mixing and hence the foam-mixing unit is water-cooled.
5.4
Coating polymers for technical textile yarns
The coating compounds are formulated on the basis of rubber or film forming synthetic polymers with solvent and water being used as the second phase. The synthetic polymer dispersions and solutions used as coating compounds
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are manufactured on the basis of urethanes, esters, vinyl chlorides, etc. Natural latex is the only natural product in this range. The chemical and physical properties of the dispersions vary according to the application area. An important step in the production of technical packtech products and protective textiles is the finishing of the substrate, especially by coating. The minimum film formation temperatures, hardness and elasticity of the films, as well as their resistance to water and to organic solvents, must not be ignored while selecting the proper coating polymer. Some of the functional finishes and coating polymers are illustrated in Table 5.2.
5.4.1 Polyvinyl chloride (PVC) Polyvinyl chloride (PVC) is the most commonly used polymer in coating textiles. This polymer is manufactured from the free radical polymerization Table 5.2 Functional polymers and their uses in various textile coatings Technical property in substrate
Coating materials
Stain release, soil release, water repellence, hot oil repellence/ resistance, waterproofing Deodorant/anti-bacterial property UV protection Fire resistance, fire retardancy Flame retardancy Water and oil repellence Chemical odour absorption Chemical protection Thermal regulation coating Thermal resistance and insulation Solvent resistance, abrasion resistance, low temperature crack resistance, ageing resistance, ozone resistance Waterproofing, electrical encapsulation, sealants Electrical conductivity, electro- magnetic (EMI) shielding, radio frequency (RFI) shielding Conductive and anti-static coating Fouling resistance Better evenness of staple fibre yarn Reinforced adhesive coated yarns
Polyvinyl chloride (PVC), vinyl acetate, perfluoro chemicals, polyacrylates, silicone based products Chitosan, poly(hexamethylene biguanide hydrochloride) – PHMB, cyclodextrin, plasma UV stabilizers Vinyl polymers Bromo phosphorus compounds, polyvinylidene chloride (PVDC) PTFE (Teflon) Activated carbon based products Based on aramid, PTFE (Teflon), carbon, neoprene coatings Phase change coatings PVC, Teflon, carbon, silicon rubber Polyurethane (PU) coating
Butadiene polyurethane resin Silver, silver/copper, silver/copper/nickel, silver/copper/tin, gold, carbon nanotubes, polyaniline (PANI) Carbon nanotubes High-density polyethylene (HDPE) Polysiloxanes, polyurethanes, polyolefins, polyacrylates or polyvinyl compounds Ethylene vinyl acetate (EVA), polyester, polyamide
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of vinyl chloride. It is a hard rigid solid that, if used as a coating material for technical textiles, needs to be changed to a soft flexible film. This is possible because of a remarkable property of PVC, the ability of the powdered polymer to absorb large quantities of non-volatile organic liquids, known as plasticizers. Plasticized PVC forms a clear film which shows good abrasion resistance and low permeability. The film may be pigmented or filled with flame-retardant chemicals to produce coloured products of low flammability. The coatings are resistant to acids and alkalis but organic solvents can extract the plasticizer, making the coatings more rigid and prone to cracking. 4 One great advantage of a polymer with an asymmetric chlorine atom is its large dipole and high dielectric strength. This means that the coated product may be joined together by both radiofrequency and dielectric welding techniques. This factor combined with its low price makes it ideal for protective sheetings such as tarpaulins, where its low permeability and good weathering properties make it a very cost-effective product. However, in the case of PVC coatings, despite the outstanding price performance ratios of PVC coatings on technical textiles, there is an increasing interest in alternatives that do not contain chlorine, because of their ecological acceptance. Monomeric vinyl chloride is carcinogenic and there are problems with the recycling process due to the chlorine. Hydrogen chloride is released and a build-up of dioxin is possible under unfavourable conditions. Chlorine-free coatings, for instance polyacrylates and polyurethanes, have already been successfully applied. However, the new replacement coatings with equivalent properties to those of PVC have not been able to achieve the economic efficiency of PVC. Polyvinyl chlorides are used to make waterproof garments, industrial clothing that is resistant to oil, grease and chemicals, and sturdy bags.
5.4.2 Polyvinylidene chloride (PVDC) PVDC is very similar to PVC. As in the case of PVC it is made by the emulsion polymerization of vinylidene chloride. The resulting polymer forms a film of low permeability to gases; however, the polymer is more expensive than PVC and therefore tends to be used only where flame resistance is required. PVDC contains twice the amount of chlorine as PVC and this extra chlorine is used in flame-resistant coatings. When a flame heats these materials, the polymer produces chlorine radicals which act as free radical traps, thus helping to snuff out the flame.
5.4.3 Polyurethanes (PU) Polyurethanes are made by the reaction of a diisocyanate with a diol as shown in Fig. 5.1. The particular diisocyanate shown is 2,4-toluene diisocyanate and
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CH3 NCO +
OH
OH
NCO
CH3 NH.CO.O
NH.CO.O
n
5.1 Polyurethane.
the diol is pentane diol but any of the analogues may be used. Polyurethanes used for coating textiles are not quite as simple as the one illustrated and the materials are frequently supplied as an isocyanate-tipped prepolymer and a low molecular weight hydroxyl-tipped polyester, polyether or polyamide. The two materials will react at room temperature although the reaction is often accelerated by raising the temperature. The only drawback to this system is that once the components are mixed, crosslinking starts immediately and so the pot life of the system is limited. Stable prepolymers which contain a blocked diisocyanate usually as a bisulfite adduct are now available. These blocked isocyanates will not react at room temperature, but will react at elevated temperatures in the presence of organotin catalysts. Polyurethane coatings show outstanding resistance to abrasion combined with good resistance to water and solvents; in addition they offer good flexibility. The chemistry of the diol can be varied considerably so as to convey water vapour permeability to the coating. PU-coated textile offers the following advantages over other polymeric coatings: ∑ ∑ ∑
dry cleanability, as no plasticizers are used low temperature flexibility overall toughness – very high tensile strength, tear strength and abrasion resistance, requiring much less coating weight ∑ softer handle.
5.4.4 Polytetrafluoroethylene (PTFE) PTFE, commercially known as Teflon, is perhaps the most exotic of the polymers that occur in coated textiles. It is manufactured by the addition © Woodhead Publishing Limited, 2010
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polymerization of tetrafluoroethylene. Since its discovery by DuPont in 1941, PTFE has found many uses in coating, particularly in the protection of fabrics from the harmful effects of sunlight. One remarkable feature of the polymer is its very low surface energy, which means that the surface cannot be wetted by either water or oil. Textile surfaces treated with this polymer are both water repellent and oil repellent. Hence PTFE is found on diverse substrates ranging from conveyor belts used in food manufacture to carpets where stain resistance is required. In addition the polymer shows excellent thermal stability and may be used up to a temperature of 250°C. PTFE-coated fabrics are high-strength materials that are used to make seals, gaskets, and stain-repellent and thermal-resistant clothing. PTFE is resistant to most solvents and chemicals, although it may be etched by the use of strong oxidizing acids; this latter fact may be used to promote adhesion. In many ways PTFE could be regarded as an ideal polymer, the main drawback to its use being its very high cost compared to the other coating materials. In order to reduce the cost of fluoropolymers several less expensive compounds have been produced, such as polyvinyl fluoride (PVF) and polyvinylidene fluoride (PVDF), which are analogous to the corresponding PVC and PVDC. However, while these materials are similar to PTFE they are slightly inferior in terms of resistance to weathering.
5.4.5 Acrylic polymers Acrylic polymers are commonly known as acrylics. The monomers are esters of acrylic and methacrylic acid. Their formula is given in Fig. 5.2. This is the general formula of acrylates (R = H for acrylates, R = CH3 for methacrylates). Some common esters are methyl, ethyl, n-butyl, isobutyl, 2-ethyl hexyl, and octyl. The esters can contain functional groups such as hydroxyl, amino and amido. The monomers can be multifunctional as well, such as trimethylol propane triacrylate or butylene glycol diacrylate. The nature of the R and R¢ groups determines the properties of monomers and their polymers. Polymers of this class are noted for their outstanding clarity and stability of their properties upon ageing under severe service conditions. Polymerization of the monomers occurs by free radical polymerization using free radical initiators, such as azo compounds or peroxides. Acrylic H
R C
H
C C
OR¢
O
5.2 Acrylic ester. R = H for acrylates, R = CH3 for methacrylates.
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polymers tend to be soft and tacky, while methacrylate polymers are hard and brittle. A proper adjustment of the amount of each type of monomer yields polymers of desirable hardness or flexibility. The vast majority of commercially available acrylic polymers are copolymers of acrylic and methacrylic esters. The polymerization can occur by bulk, solution, emulsion and suspension methods. The suspension-grade polymer is used for moulding powders. The emulsion and solution grades are used for coatings and adhesives. Acrylate emulsions are extensively used as thickeners and for coatings. Acrylics have exceptional resistance to UV light, heat, ozone, chemicals, water, stiffening on ageing, and dry-cleaning solvents. As such, acrylics are used as backcoating materials in automotive upholstery fabric and carpets, window drapes, and pile fabrics used for outerwear.
5.4.6 Polyaniline (PANI) Polyaniline (PANI) is a conducting polymer of the semi-flexible rod polymer family. Although it was discovered over 150 years ago, only recently has polyaniline captured the attention of the scientific community due to the discovery of its high electrical conductivity. Nowadays it is being used in conductive coating of yarns in making intelligent and multifunctional yarns. Amongst the family of conducting polymers, polyaniline is unique due to its ease of synthesis, environmental stability and simple doping/dedoping chemistry. Although the synthetic methods to produce polyaniline are quite simple, its mechanism of polymerization and the exact nature of its oxidation chemistry are quite complex. Because of its rich chemistry, polyaniline has been one of the most studied conducting polymers of the past 20 years.5 Polymerized from the aniline monomer, polyaniline can be found in one of three idealized oxidation states:6 ∑ ∑ ∑
leucoemeraldine emeraldine pernigraniline.
In Fig. 5.3, x equals half the degree of polymerization (DP). Leucoemeraldine with n = 1, m = 0 is the fully reduced state. Pernigraniline is the fully oxidized state (n = 0, m = 1) with imine links instead of amine links. The emeraldine (n = m = 0.5) form of polyaniline, often referred to as emeraldine base (EB),
N
N
N n
H
H
5.3 Main polyaniline structures: n + m = 1, x = degree of polymerization.
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is either neutral or doped, with the imine nitrogens protonated by an acid. Emeraldine base is regarded as the most useful form of polyaniline due to its high stability at room temperature and the fact that upon doping the emeraldine salt form of polyaniline is electrically conducting. Leucoemeraldine and pernigraniline are poor conductors, even when doped with an acid. An important property of polyaniline is its electrical conductivity, which makes it suitable for such purposes as the manufacture of electrically conducting yarns, antistatic coatings, electromagnetic shielding and flexible electrodes.
5.4.7 Rubber7 Rubber is a preferred material for coating for two reasons: ∑ It is resistant to mechanical wear and tear. ∑ It is resistant to the influence of strongly aggressive environments. The rubber coating application is a very important consideration in the selection of the coating material. The purpose of the coating and the kind of rubber required for the coating are chosen according to the kind of technological equipment. The design of the application is chosen considering both the equipment exploitation and equipment design departments. Yarns can be rubber coated by extrusion coating, roller coating or dipping. Rubber coatings provide a barrier against the leaching of elastomeric by-products, and at the same time protect surfaces from organic solvents and inorganic reagents, acids and solutions. The following types of rubber are used for coating textiles: ∑ Natural rubber ∑ Silicone rubber (SiR) ∑ Polychloroprene (CR)/neoprene ∑ Ethylene propylene diene monomer (EPM, EPDM) ∑ Fluoroelastomers (FKM)/viton ∑ Styrene–butadiene rubber (SBR) ∑ Nitrile rubber ∑ Butyl rubber (IIR) ∑ Chlorosulfonated polyethylene (CSM)/hypalon. Natural rubber While synthetic or artificial rubber is produced from petroleum, around onequarter of the world’s rubber comes from natural sources. Natural rubber is a vital agricultural product or commodity which is used in the manufacture of a wide range of products. It is produced from hundreds of different plant species. However, the most important source is from a tropical tree known © Woodhead Publishing Limited, 2010
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as Hevea brasiliensis, which is native to the tropical Americas. Natural rubber is available in many grades and the most important distinction is that between latex and solid grades. Latex is the liquid that comes out of the tree. Solid grades are produced from latex that has coagulated either in a factory or in the field. Natural rubber latex products are widespread and varied, including gloves, balloons, tubes, condoms, etc. Rubber occurs as an emulsion, which may be used directly for coating, or the polymer may be coagulated and mixed at moderate temperatures with appropriate fillers. Natural rubber is a linear polymer of polyisoprene. The formula (see Fig. 5.4) shows that the natural polymer contains unsaturated double bonds along the polymer chain. Natural rubber has certain unique properties as follows: ∑ ∑
High strength (tensile and tear) with outstanding resistance to fatigue Excellent green strength and tack, which means that it has the ability to stick to itself and to other materials which makes it easier to fabricate ∑ Moderate resistance to environmental damage by heat, light and ozone, which is one of its drawbacks ∑ Excellent adhesion to brass-plated steel cord, which is ideal in rubber tyres ∑ Low hysteresis which leads to low heat generation, this in turn maintaining new tyre service integrity and extending retreadability. Silicone rubber (SiR) Silicone rubber is a synthetic polymer that has a backbone of silicon–oxygen linkages called siloxane links Si—O—Si that are formed by the condensation of the appropriate silanol which is formed from the halide or alkoxy intermediate; the final condensation then takes place by the elimination shown in Fig. 5.5. H
H C H
C
H
H
C
C H
CH3
C
C
H
CH3
H
H
C
C H
n
5.4 Polyisoprene (rubber). R1 OH
Si R2
R1 OH
O
Si R2
R1 O
Si R2
n
5.5 Silicone rubber. R1 and R2 are unreactive alkyl or aryl groups.
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This rubber has a similar bond structure to that found in glass, sand and quartz. It is a unique synthetic elastomer that is made from a crosslinked polymer reinforced with silica. The characteristic of this rubber is such that it provides the perfect balance of mechanical and chemical properties which is required in today’s most demanding applications. Silicone rubber has the following properties: ∑
The outstanding property of this form of rubber is its very wide temperature range. It offers excellent resistance to extreme temperatures, the range of which can be from –100°F (–73°C) to +500°F (+260°C). ∑ It is resistant to many chemicals, oils, acids and gases. ∑ Because of its compatibility with a wide temperature range, the tensile strength, elongation, tear strength and compression set of this rubber can be far superior to those of conventional rubbers. ∑ It is, however, susceptible to ozone, UV, heat and other ageing factors. ∑ It is electrically conductive and metal-detectable and glows in the dark. ∑ It has low smoke emission and it is flame retardant. Polychloroprene (CR)/neoprene Polychloroprene rubber (CR) is the polymer name for the synthetic rubber known as neoprene. This rubber was developed in 1931 and is supposed to be the first of the speciality elastomers. It is one of the most important types of synthetic rubber with an annual consumption of nearly 300,000 tons worldwide. This rubber has a good balance of mechanical properties and fatigue resistance which is second only to that of natural rubber, but has superior oil, chemical and heat resistance. Neoprene, an extremely versatile synthetic rubber, is the DuPont Performance Elastomers trade name for a family of polychloroprenes. Neoprene has more than 75 years of proven performance in a broad industry spectrum. Its chemical structure is shown in Fig. 5.6. Neoprene rubber has no single outstanding property, but its balance of properties is unique among the various types of synthetic rubber. It has the following properties: H
H
C
C
H
H
H
H
C
C
C
C
Cl
H
H
H C
C
Cl
H
n
5.6 Polychloroprene (neoprene).
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∑ Good mechanical strength, high ozone and weather resistance ∑ Good ageing resistance ∑ Low flammability and good resistance towards chemicals ∑ Moderate oil and fuel resistance ∑ Adhesion to many substrates. Ethylene propylene diene monomer (EPM, EPDM) Ethylene propylene rubber is used for many purposes. It is considered to be the most water-resistant rubber available and is widely used for the manufacture of sheeting that is to be used at high temperatures. This is one of the most commonly used and fastest growing synthetic rubbers, having both general-purpose and speciality applications. According to a report in 2000, sales of this rubber had grown to 870 kilotonne or 1.9 billion pounds.8 Commercial application of this rubber started in 1960. It is to be noted that the abbreviation of this rubber is EPM or EPDM which means that the rubber consists of ethylene and propylene (EPM), but the letter D tells us that a diene is also present (EPDM). The third monomer, diene, makes it possible to cure the rubber with sulfur since it introduces double bonds in the structure which change the structure to an unsaturated polymer (see Fig. 5.7). Ethylene propylene diene monomer has the following properties: ∑ Excellent resistance to atmospheric ageing and oxygen ∑ Good resistance to ozone and to most water-based chemicals ∑ Resistance to vegetable-based hydraulic oils ∑ Very poor resistance to mineral oils and diester based lubricants
H
H
H
H
C
C
C
C
H
H x
CH3 H y
(a) EPM
Dicyclopentadiene
Ethylidene norbornene (b)
trans-1,4-Hexadiene
5.7 (a) Ethylene propylene monomer (EPM); (b) some dienes.
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∑ ∑
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A stable, saturated polymer backbone structure Excellent resistance to heat and good electrical resistivity.
Fluoroelastomers (FKM)/Viton This is a class of synthetic rubbers designed for very high temperature operation. FKM provide extraordinary levels of resistance to chemicals, heat and oil, while providing a useful service life above 200°C. FKM are not a single entity but a family of fluoropolymer rubbers. Fluoroelastomers or FKM can be classified by their fluorine content, 66%, 68% and 70%, respectively. A higher fluorine content gives FKM rubber increasing fluid resistance. The properties of fluoroelastomers (FKM) are as follows: ∑
They have excellent resistance to chemical attack by oxidation, by acids and by fuels, and they have good oil resistance. ∑ They have limited resistance to steam, hot water, methanol and other highly polar fluids. ∑ The outstanding heat stability and excellent oil resistance are due to the high ratio of fluorine to hydrogen, the strength of the carbon–fluorine bond, and the absence of unsaturation. Styrene–butadiene rubber (SBR) SBR is made by the emulsion polymerization of styrene and butadiene as illustrated in Fig. 5.8. The formula illustrated implies a regular copolymer but this is not the case and SBR is a random copolymer. The compounding and application techniques are very similar to those for natural rubber although
C
H
H
H
H
+
C
C
C
H
H
H
H
H
H
C
C
C
C
H
H
H C H
C H
H C
C
H
H n
5.8 Styrene–butadiene rubber (SBR).
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the material is not as resilient as natural rubber and also has a greater heat build-up, which make SBR inferior to natural rubber in tyres. In the case of coated fabrics, the superior weatherability and ozone resistance of SBR, combined with the ease of processing, make this the product of choice. It is estimated that 50% of all rubber used is SBR. Nitrile rubber Nitrile rubbers are copolymers of acrylonitrile and butadiene as shown in Fig. 5.9. These materials are used primarily for their excellent oil resistance, which varies with the percentage acrylonitrile present in the copolymer, and show good tensile strength and abrasion resistance after immersion in oil or petrol. They are not suitable for car tyres but are extensively used in the construction of flexible fuel tanks and fuel hose. Butyl rubber (IIR) Butyl rubber (IIR), the chemical name of which is isobutylene–isoprene copolymer, is actually the copolymer of isobutylene and a small amount of isoprene (Fig. 5.10). This rubber was first commercialized in 1943. Resulting from low levels of unsaturation between long polyisobutylene segments, the primary attributes of butyl rubber are excellent impermeability/air retention and good flex properties. The first major use of butyl rubber was for tyre inner tubes, and this continues to be a significant market today. Chlorosulfonated polyethylene (CSM)/hypalon Chlorosulfonated polyethylene is a synthetic rubber based on polyethylene. This rubber is a material with neoprene polychloroprene plus other qualities. H
H C
H
H
H +
C
C
H
C
C
H
CN
C H
H
H
H
H
H
C
C
C
C
H
CN
H
H C
C
H
H
n
5.9 Nitrile rubber.
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H C
+
C
CH3
CH3
H C
H
C
C
H
CH3 H
H
CH3
C
C
C
C
CH3 H
H
H C
H
H
H C
C
H
H
n
5.10 Butyl rubber.
CSM rubber is suitable for continuous use up to about 130°C and intermittent use up to some 30°C above this. Chlorosulfonated polyethylene has shown long life in harsh environments and is used in a variety of industrial and automotive applications that require high performance. Its properties are as follows: ∑
Excellent resistance to oxygen, ozone and most chemicals, including water ∑ Poor fuel resistance and low gas permeability ∑ Resistance to weather and abrasion. Chlorosulfonated polyethylene is used in adhesives, insulation, flexible tubes, seals, flexible magnetic binders, industrial products such as hose, rolls, seals, gaskets, diaphragms and linings for chemical processing equipment and a variety of protective and decorative coatings.
5.4.8 Nylons Nylon is the common name of linear aliphatic polyamides. The most important in this class are nylon 6,6 and nylon 6. Nylon 6,6 is polyhexamethylene adipamide, a condensation polymer of hexamethylene diamine and adipic acid. The suffix 6,6 stands for the number of carbon atoms in the monomers. Nylon 6 is polycaprolactamide, the monomer being e-caprolactam. The reaction sequences are given in Fig. 5.11. Polyamide nylon types are often referred to as high performance hot melt coatings and are used for more demanding product assembly applications. Polyamide adhesives are well known for their ability to adhere to textile substrates. They have a relatively high and sharp melting point along with high shear resistance. The sharp melting point allows easy application at higher temperatures with faster bonding upon cooling. These adhesives have
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+
nHOOC(CH2)4COOH
Hexamethylene diamine
—[NH(CH2)6—NH—CO—(CH2)4—CO]n—
Adipic acid
Nylon 6,6
(CH2)5 NH
157
—[NH(CH2)5—CO—]n— CO Nylon 6
e-Caprolactam
5.11 Nylon 6,6 and nylon 6.
COOCH3 + nHO—CH2—CH2—OH
nCH3OOC Dimethyl terephthalate
OCH2CH2OOC
Ethylene glycol
OCH2CH2OH
CO n
Polyethylene terephthalate
5.12 Polyethylene terephthalate.
excellent resistance to washing and dry-cleaning solvents. Further details are given at http://www.enyarns.com/polyamide.html.
5.4.9 Polyesters Polyester refers to a class of polymers containing a number of repeat ester groups in the polymeric chain. Commercially available polyester fibre is polyethylene terephthalate (Fig. 5.12). It is known in different countries by different brand names. In the UK it is known as Terylene and in the US as Dacron. The fibre is available in filament as well as in staple fibre form. A number of other polyesters have been converted into fibres, but they have not been exploited commercially. In coating, polyesters offer excellent adhesion, great wash resistance, and resistance to dry-cleaning solvents. Reinforced polyester adhesives also offer excellent resistance to plasticizer migration, with high tensile strengths and fast set times.
5.4.10 Ethylene vinyl acetate9 Ethylene vinyl acetate (known as EVA) is the copolymer of ethylene and vinyl acetate. The weight percent of vinyl acetate usually varies from 10%
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to 40%, with the remainder being ethylene. (Fig. 5.13). It is a polymer that approaches elastomeric materials in softness and flexibility, yet can be processed like other thermoplastics. The material has good clarity and gloss, barrier properties, low-temperature toughness, stress-crack resistance, hotmelt adhesive waterproof properties, and resistance to UV radiation. EVA has little or no odour and is competitive with rubber and vinyl products in many electrical applications. Hot-melt adhesives, hot glue sticks, are usually made from EVA, usually with additives like wax and resin. EVA is also used in biomedical engineering applications as a drug delivery device. EVA is one of the materials popularly known as ‘expanded rubber’ or ‘foam rubber’. EVA foam is used as padding in equipment for various sports such as ski boots, hockey, boxing, mixed martial arts, wakeboard boots, and waterski boots. It is typically used as a shock absorber in sports shoes, for example. EVA can be recognized in many Holeys (Vancouver, Canada) brands of shoes and accessories, in the form of a foam called Smartcel™. EVA slippers and sandals are nowadays very popular because of such properties of EVA as light weight, ease of moulding, lack of odour, glossy finish, and cheapness compared to natural rubber. Ethylene vinyl acetate is mainly recognized for its economy, flexibility, toughness, adhesion characteristics, and stress-crack resistance.
5.4.11 Chitosan In recent years, great attention has been devoted to biopolymers because of their biocompatibility and biological functions and consequently their potential application in the biomedical and pharmaceutical fields. In this regard, chitosan has a great potential for a wide range of uses due to its biodegradability, biocompatibility, antimicrobial activity, non-toxicity and ability to improve wound healing, and therefore it is evaluated in a number of medical applications. Chemically, chitosan (Fig. 5.14) is a linear polysaccharide composed of randomly distributed b-(1-4)-linked d-glucosamine (deacetylated unit) and N-acetyl-d-glucosamine (acetylated unit). Chitosan is produced commercially by deacetylation of chitin, which is the structural element in the exoskeleton of crustaceans (crabs, shrimps, etc.).10 H3 C O
C
H
H
H
O
C
C
C
C
H
H
H
H
n
m
5.13 Ethylene vinyl acetate.
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CH2OH
O OH
CH2OH O
O O
OH
159
OH
OH
O
OH NH2
NH2
n
NH2
5.14 Chitosan.
Chitosan’s properties allow it to rapidly clot blood, and it has recently gained approval in the USA for use in bandages and other haemostatic agents. Chitosan purified from shrimp shells is used in a granular haemostatic product, Celox. Celox has been shown in testing by the US Marines to quickly stop bleeding and result in 100% survival of otherwise lethal arterial wounds and to reduce blood loss. The Hemcon product reduces blood loss in comparison to gauze dressings and increases patient survival. Hemcon products have been sold to the US Army, who have already used the bandages on the battlefields of Iraq. Chitosan is hypoallergenic and has natural antibacterial properties, further supporting its use in the medical field.
5.4.12 Carbon nanotubes (CNTs) Carbon nanotubes – long, thin cylinders of carbon – were discovered in 1991 by the Japanese scientist Sumio Iijima.11 These are large macromolecules and are unique for their size, shape and remarkable physical properties (see Fig. 5.15). They can be thought of as a sheet of graphite (a hexagonal lattice of carbon) rolled into a cylinder with a hollow interior. The length of the nanotube may be tens of thousands times bigger than its diameter. Depending on the number of carbon layers, a distinction is made between single-walled (SWNT) and multi-walled carbon nanotubes (MWNT). They are usually made by carbon-arc discharge, laser ablation of carbon, or chemical vapour deposition. Their diameter may vary between 0.4 and several nanometres; their length may be several hundred microns. The structure of a carbon nanotube is like a sheet of graphite rolled up into a tube. Depending on the direction of the hexagons, nanotubes can be classified as either zigzag, armchair or chiral. (Fig. 5.16).12 Different types of nanotubes have different properties. When scientists make nanotubes, they tend to get a mixture of several types. A major challenge in nanoscience today is finding a way to make just one type of nanotube. The intriguing structures of CNTs have sparked much excitement in recent years and a large amount of research has been dedicated to their understanding. Currently, the physical properties are still being discovered and disputed. What makes it so difficult is that nanotubes have a very broad
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10–20 nm
(a)
(b)
5.15 (a) Scanning electron micrograph (SEM) of carbon nanotube bundles. Magnification was about 7220¥; the frame covers about 15 micrometres in the horizontal axis (1 micrometre = 1 millionth of a metre). The nanotubes themselves are roughly 10 nanometres (10 billionths of a metre) in diameter. (b) Transmission electron micrograph (TEM) of carbon nanotube bundles showing bundles 10–20 nm wide.
(a)
(b)
(c)
5.16 Structures of carbon nanotubes: (a) armchair, (b) zigzag, (c) chiral (Ref. 12).
range of electronic, thermal and structural properties that change depending on the different kinds of nanotube (defined by their diameter, length, and chirality or twist). To make things more interesting, besides having a single
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cylindrical wall (SWNTs), nanotubes can have multiple walls (MWNTs) – cylinders inside the other cylinders13 (Fig. 5.17). Due to their many interesting properties, carbon nanotubes are appropriate for use in a wide range of applications. In this respect, they are 100 times stronger than steel while weighing six times less, and being one giant molecule, carbon nanotubes have unusual and extraordinarily good mechanical, electrical and thermal properties. The conductivity of single-wall carbon nanotubes can vary from semi-conductive to metallic depending on the chiral angle of the tube and its diameter. Numerical simulations predict the Young’s modulus of single-wall nanotubes to be in excess of a terapascal (TPa). Because of their exceptionally high length/diameter ratio, a very interesting prospect for CNTs is processing in combination with polymers for the production of composite structures. Even when only small quantities of CNTs are applied, their exceptional properties are already transferred onto the composite material. It is therefore obvious that CNTs – if correctly processed – will create an important added value in different textile applications. The percentage of CNT needed to introduce conductivity into a composite material varies between 0.5% and 4.5%, depending on their dispersion, the desired level of conductivity and the final application. Although the material costs of CNTs are still very high, prices are decreasing because of increased production capacity. Researchers have recently verified the applicability of CNTs as an additive in both polymer melt processing and textile coating and finishing applications.14 Researches proved that it is possible to produce conductive and antistatic textile materials including fibre, yarn and fabric by coating CNTs. The level of conductivity depends on the application method (extrusion, coating, textile finishing) and the desired end product:
(a)
(b)
5.17 (a) Single-walled (SWNT) and (b) multi-walled carbon nanotubes (MWNT) (Ref. 13).
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∑ ∑
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Conductive textiles (resistance from 10 to 106 Ω/sq) Antistatic textiles (resistance from 106 to 1012 Ω/sq).
Further research is needed to apply CNTs in industrial processes. Constant modifications of carbon nanotubes will indeed lead to improved product properties. One of the main points of interest is the dispersion level. Further optimization of the extrusion conditions and of the textile coating and finishing formulas is therefore extremely important. Nanocoated textile fibres and yarns are produced by depositing layers of a coating onto the surface of the substrates. The thickness of each layer is in the nanometre range. A number of methods have been used to apply a nanocoating to the fibre surface. For commercially available products, Nano-Tex,15 founded in 1998, has been one of the leaders in nano-treatments designed specifically for textiles. The first commercially available products were released to the market in December 2000. Today, more than 80 textile mills around the world are utilizing Nanotex’s patented nano-treatments. Nano-Tex treatments are applied to a textile substrate in a ‘bath’. As the substrate goes through the bath, nanoparticles come into contact with the fibres of the fabric. When the substrate is cured or heated – the nanoparticles spread out evenly and bond to the fibres. Treatments are permanent and do not jeopardize the aesthetic characteristics or mechanical properties of the substrate. Treatments can be applied to a number of fibres including cotton, polyester, silk and wool. A variety of enhancing characteristics can be imparted to the substrate through the application of special treatments. Nano-treated materials can be spill resistant, stainproof, wrinkle resistant and static-proof.
5.5
Choice of substrates for yarn coating
There is no unique solution to substrate (yarn) or polymer choice in coatings, because different materials can be used to achieve similar results in the end product. The manufacturer’s choice of polymer is affected by polymer properties, polymer availability, cost analysis, coating equipment to be used, tradition and environmental protection. But the main goal to achieve a particular property of yarn by coating and some additional characteristics may be obtained by the same coating. Yarns used for coating are mainly artificial fibres such as nylon, polyester, aramid, high molecular weight polyethylene (HMPE), fibreglass, carbon and so on. But yarns made of staple yarns are also coated to ease the weaving and knitting process or to make multifunctional yarns: for details see Section 5.8.
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Principles of yarn coating
5.6.1 Solvent coating Solvent coating systems may be used for many coated technical yarns. The polymer is dissolved or dispersed in an organic solvent (or mixture of solvents) to give a viscous material that can be applied to the surface of the yarns. Because the solvent content may be as high as 40% by weight of the coating composition, evaporation of the solvent in the thermal fluid-heated oven is generally followed by either a solvent recovery/recycling process or the solvent vapour is led into the boiler combustion chamber and burned to recover the heat. Operators must carefully control and regulate drying and curing ovens for solvent coating in order to run the machine outside the air/solvent concentration explosive limits. Health and safety are paramount in solvent coating, and adequate venting and design of the drying oven to operate under safe working conditions and automated process control are essential.
5.6.2 Aqueous coating Aqueous-based coating systems are also used to apply water-soluble/waterdispersable polymers to the yarns. The coating formulation must be dried by evaporation of the water in a hot air oven (drying machine) that may be heated by combustion of gas directly in the chamber, or by hot air heated indirectly through a heat exchanger. Thermal drying consumes considerable energy because of the high latent heat of vaporization of water compared with organic solvents. Accordingly, process monitoring and control of the hot exhaust air and of the inlet air are necessary to operate the dryer in the most appropriate humidity range. Efficient door sealing, thick thermal insulation of the dryer, and air-to-air or air-to-water heat recovery may be fitted to the dryer. Hot exhaust air from the dryer may thus be used to heat incoming fresh air entering the dryer, or used to generate hot water for use in wet processing. Some types of technical yarns are totally immersed in a coating formulation. The impregnated yarn is squeezed in a pad mangle to a constant pick-up (that is, weight of coating as a percentage based on air-dry fabric weight) and then dried in a hot air stenter at constant width, followed by batching on to a roller. Aqueous polymer systems commonly used for impregnation of yarn include: ∑ Urethane ∑ Acrylic ∑ Epoxy
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∑ Fluorocarbons ∑ Nylon.
5.6.3 Hot-melt coating Hot-melt coating involves either calendering the molten thermoplastic polymer directly on the textile using a pair of calender bowls (rollers), or in some cases the molten polymer is extruded directly onto the textile from a slotted die in a process called extrusion coating. After this a smooth coating is obtained by contact with a polished chill roller. Hot-melt coated yarns are a unique combination of adhesive and yarn reinforcement that is customized to meet exacting application requirements. Through proper selection of resin, coating level and yarn, a coated yarn can be optimized for adhesion and reinforcement properties. Resins are selected for their adhesive properties and temperature characteristics. They are generally ethylene vinyl acetates, polyamides, polyesters and polyurethane. Solution-dyed multifilament cores can be used for colour coding. Hot-melt yarns are typically used where a metered amount of adhesive is desired. These products allow for less demanding application needs since there is no need to deal with hot, viscous resin baths and their associated application equipment. Improved economics are also an advantage since there is no equipment clean-up or waste. Yarn application systems are less complex, clean operating, and generally inexpensive. Hot-melt adhesives are thermoplastics, based on polymers that become liquid between temperatures of 80 and 220°C and solidify again by cooling down. They consist of 100% dry substance and are applied in a liquid state without using water or solvents. Due to the process only a short binding and setting time is required in comparison with dispersions or solutions. The advantages of hot melt coatings are as follows: ∑ ∑ ∑ ∑ ∑ ∑
Environmentally friendly due to water and solvent-free adhesives low coating weight needed Elimination of dryer/low energy requirements no thermal stress of substrate high production speed possible permanent or non-permanent adhesive coatings possible.
Polymer systems usually used for hot-melt and extrusion coating of yarn include: ∑ Polyester elastomer ∑ Nylon ∑ Polypropylene ∑ Ethylene vinyl acetate (EVA)
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∑ Polyvinylidene fluoride ∑ Ionomer ∑ Thermoplastic urethane.
5.6.4 Metal coating Conductive fibres and yarns have attracted considerable attention during the last decade. Generally speaking, textile materials made of organic polymers are perfect insulators. Due to their weak electrical conductivity, electrical load is accumulated on the surface of organic polymers. Therefore, to prevent the accumulation of electrical load, to enhance the possibility of electrical load transfer and to obtain an electromagnetic shielding effect, the textile materials have been turned into electrical conductors by using different methods, including coating yarns with conductive substances. Conductive coated yarns and filaments of this kind are used in many application areas. By utilizing the conductive yarns in the fabric structures, various functionalities may be attributed to the fabrics. Enhancing both the properties of textile structures and the function of conductivity, conductive textiles have important applications not only in medical and military fields, but also in the fields of fashion, architecture and design for their aesthetic appeal. Therefore textiles with a conductivity function are used in many technical applications such as protection of people and electronic devices from electromagnetic interference (EMI) and electrostatic discharge, heating, wearable electronics, data storage and transmission, sensors and actuators. Textiles are being increasingly studied with a view to using them as sensing and measuring devices of body parameters such as heart rate, temperature or sweat, on a continuous basis. For this purpose they need to be modified by coating to provide reliable electroconductive properties. Research has been conducted to polymerize conductive polymers, such as polypyrrole and polyaniline, on different yarn substrates, but these inherently conductive polymers offer limited conductivity in the range of a semiconductor. Therefore various researchers have applied metal coatings, such as copper, gold, silver and nickel, directly to textile yarns to offer excellent electrical conductivity and inertness with biocompatibility (Fig. 5.18).16 Metal coating with a binder The process is similar to conventional polymer coating. High leafing metal pastes (65–70%) are incorporated into a polymeric carrier, such as synthetic rubber, PVC, polyurethanes, silicones, acrylic emulsions, etc., and coated on the yarns. The coating method may be conventional knife or roller coating. The adhesion, flex and chemical resistance of the coated material depend on the type of polymer used.
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Technical textile yarns Copper layer
Paraaramid
Polypyrrole (PPy)
5.18 Schematic representation of a single polypyrrole and coppercoated para-aramid fibre (adapted from Ref. 16).
Vacuum coating Vacuum coating or vacuum deposition is a family of processes used to deposit layers atom-by-atom or molecule-by-molecule at sub-atmospheric pressure (vacuum) on a solid surface. The layers may be as thin as one atom to millimetres thick (freestanding structures). There may be multiple layers of different materials (e.g. optical coatings). Condensing particles may come from a variety of sources, including: ∑ thermal evaporation, evaporation (deposition) ∑ sputtering ∑ cathodic arc vaporization ∑ laser ablation ∑ decomposition of a chemical vapour precursor, chemical vapour deposition (CVD). When the vapour source is from a liquid or solid material the process is called physical vapour deposition (PVD). When the source is from a chemical vapour precursor the process is called low pressure chemical vapour deposition (LPCVD) or, if in a plasma, plasma enhanced CVD (PECVD) or ‘plasma assisted CVD’ (PACVD). Often a combination of PVD and CVD processes is used in the same or connected processing chambers. ∑
Evaporation (deposition): Evaporation is a common method of thin film deposition. The source material is evaporated in a vacuum. The vacuum allows vapour particles to travel directly to the substrate, where they condense back to a solid state. Evaporation is used in microfabrication, and to make macro-scale products such as metallized plastic film or yarn. ∑ Sputtering: Sputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic ions. It is commonly used for thin-film deposition, etching and analytical techniques. ∑ Cathodic arc deposition: Cathodic arc deposition or arc-PVD is a physical
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∑
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vapour deposition technique in which an electric arc is used to vaporize material from a cathode target. The vaporized material then condenses on a substrate, forming a thin film. The technique can be used to deposit metallic, ceramic and composite films. Laser ablation: Laser ablation is the process of removing material from a solid (or occasionally liquid) surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates. At high laser flux, the material is typically converted to a plasma. Usually, laser ablation refers to removing material with a pulsed laser, but it is possible to ablate material with a continuous wave laser beam if the laser intensity is high enough. Chemical vapour deposition: CVD is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films or yarns. In a typical CVD process, the substrate is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. Some metals (notably aluminium and copper) are seldom or never deposited by CVD. In this case, deposition of the metal is performed mostly by electroplating.
Plating Plating describes surface-covering where a metal is deposited on a conductive surface. Plating is used to decorate objects, for corrosion inhibition, to improve solderability, to harden, to improve wearability, to reduce friction, to improve paint adhesion, to alter conductivity, for radiation shielding, and for other purposes. Jewellery typically uses plating to give a silver or gold finish. Thin-film deposition has plated objects as small as an atom, therefore some plating is nanotechnology. Electroplating/electrodeposition In electroplating, an ionic metal is supplied with electrons to form a nonionic coating on a substrate. Electroplating uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal. A common system involves a chemical solution with the ionic form of the metal, an anode (positively charged) which may consist of the metal being plated (a soluble anode) or an insoluble anode (usually carbon, platinum, titanium, lead or steel), and finally a cathode (negatively charged) where electrons are supplied to produce a film of non-ionic metal.
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Electroless plating/deposition Electroless plating, also known as chemical or autocatalytic plating, is a plating method that involves several simultaneous reactions in an aqueous solution, which occur without the use of external electrical power. The reaction is accomplished when hydrogen is released by a reducing agent, normally sodium hypophosphite, and oxidized thus producing a negative charge on the surface of the part. Compared to electroplating, electroless coating has the advantage that it can metallize non-conducting materials and it does not require electrical energy. Electroless coating is, however, more expensive. For coating non-conductive textile fibres/yarns, electroless deposition is mostly used as most of the textile fibres are non-conductive. Some important metals for coating yarn are gold, silver, copper and nickel. ∑
Gold: In order to use textile yarns as sensing and measuring devices of body parameters, gold is an ideal material to coat the surface of a fibre, yarn or fabric. Gold-coated substrates are highly electroconductive, skin-friendly and stable. ∑ Silver: Silver is often used as a cheaper replacement for gold. But silver is actually a better conductor than gold. Since the autocatalytic activity of silver is low, thick deposits cannot be obtained. In medical engineering, antibacterial and electrically conductive yarns are of great interest. Coating yarns with silver makes them highly suitable for obtaining both properties. ∑ Copper: Copper is a good material to use in coating because of its outstanding electroconductive properties and the possibility of coating chemically and/or electrochemically on the surface of a fibre, yarn or fabric. ∑ Nickel: Nickel also has the same electroconductivity as copper. Among the above-mentioned metals, silver, copper and nickel may cause problems with the human skin. They are better electrical conductors, but are not corrosion resistant. In comparison to them, gold is an excellent material to use as a sensing material to measure body parameters as it combines both excellent electrical conductivity and inertness with biocompatibility. Gold-coated yarns possess excellent resistivity, which is close to that of pure gold.16
Plasma treatment Since the introduction of plasma technology in the 1960s, the industrial applications of low-pressure and low-temperature plasma have been mainly in microelectronic etching. In the 1980s, plasma technology was also applied
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to other material surface treatments, especially in metals and chemical polymers. Due to stringent controls on chemical finishing of textile materials, new and innovative textile treatments are demanded. In this regard, plasma technology shows distinct merits due to its environmental friendliness and better treatment results. Presently, research institutions are applying plasma technology in textile processing. The plasma is an ionized gas with equal density of positive and negative charges which exists over an extremely wide range of temperature and pressure. The plasma consists of free electrons, ions, radicals, UV radiation and other particles depending upon the gas used. The plasma gas particles are etched on the fibre surface on a nano-scale so as to modify the functional properties of the fibre. Unlike conventional wet processes, which penetrate deeply into fibres, plasma reacts only with the fibre surface so it does not affect the internal structure of the fibres. Plasma technology modifies the chemical structure as well as the topography of the textile material surface. In medical engineering, antibacterial and electrically conductive yarns are of great interest. Coating yarns with silver makes them highly suitable for obtaining both properties. But the quantity of silver applied as well as its adhesion to the yarns must be controlled in order to prevent it from being washed out and from contaminating waste water. Plasma technology is very useful here. High-energy particles are accelerated from the plasma onto a silver plate, the target. In the process, silver atoms are ejected, which produces the coating on the yarns on a nanometre scale.17 Lamination A laminated yarn can be produced by either an adhesive laminated process or an extrusion laminated process. A laminated (or combined) fabric consists of two or more layers, one of which is a textile fabric, bonded closely together using heat and pressure by means of an added adhesive, or by the adhesive properties of one or more of the component layers. Usually the layer in a laminated substrate consists of a polymeric substance; however, in some metallized yarns the metal is not deposited by chemical deposition but is laminated using an adhesive or by use of an electric arc. In most methods of making laminated yarn, yarn film is used and may be coloured with synthetic resin and special dyestuff, thus giving an outstanding effect. The coated film is then cut according to its intended purpose, slit by a micro-slitter in a fixed size, and then automatically wound on a bobbin.18
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5.7
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Methods and machinery for yarn coating
5.7.1 Knife coaters In knife coating the formulation is applied directly to the yarn sheet and spread uniformly by means of a knife (or blade) operating at a controlled fixed distance from the yarn’s surface to give a constant thickness. Yarn may be coated using coating machinery that operates on any of the following principles (see Fig. 5.19): ∑ knife on air ∑ knife over table ∑ knife over roller or gap coating ∑ knife over rubber blanket. In knife on air systems, the knife or blade is placed in direct contact with the yarn under tension, forcing the coating into the yarn. In knife over table and knife over roller coating systems the blade is at a fixed height above the yarn. This process relies on a coating being applied to the substrate, which then passes through a ‘gap’ between a ‘knife’ and a support table or roller. As the coating and substrate pass through, the excess is scraped off. This process can be used for high-viscosity coatings and very high coat weights, such as plastisols and rubber coatings. There are innumerable variants of this relatively simple process which is rugged, hard-working and somewhat inaccurate. Irregularities in the yarn sheet can create problems with the yarn jamming under the blade. In the knife over rubber blanket method there is a controlled gap, but the flexibility of the rubber blanket allows yarn irregularities to pass underneath the blade.
(a)
(b)
(c)
(d)
5.19 Knife coating: (a) knife on air, (b) knife over table, (c) knife over roller, (d) knife over blanket (adapted from Ref. 4).
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5.7.2 Air knife coating This is a simple process where the coating is applied to the substrate and the excess is ‘blown off’ by a powerful jet from the air knife. This procedure is typically used for aqueous coatings and is particularly noisy (Fig. 5.20). 19
5.7.3 Roll coaters Metering rod (mayer rod) coater 20 This is one of the most popular coating methods. It is widely used both in the laboratory and in production coaters to coat a wide variety of products. It is also one of the oldest coating methods. It was first used by Charles Mayer in 1905 and it has been in continuous use ever since. A Mayer rod coater is referred to by various names – Mayer bar, Meyer bar, Meyer rod, coating rod, equalizer bar, doctor rod – although Mayer rod is the most frequently used name. The Mayer rod is a stainless steel rod that is wound tightly with stainless steel wire of varying diameter. In this coating process, an excess of the coating is deposited onto the substrate as it passes over the bath roller. The Mayer rod is used to doctor the excess coating solution and control the coating weight (Fig. 5.21).19,20 Typical rods are shown in Fig. 5.21. The wet thickness after doctoring is controlled by the diameter of the wire used to wind the roll and is approximately 0.1 times the wire diameter. Rods are available in a wide variety of wire sizes to give a range of coating weights. Direct roll coating In direct roll (or squeeze roll) coating, a premetered quantity of the coating is applied on the fabric by controlling the quantity on the applicator roll by the doctor knife (see Fig. 5.22). The substrate moves in the same direction as the applicator roll. This method is also restricted to low viscosity compounds
Coating polymer
Air knife
Substrate
5.20 Air knife coating (adapted from Ref. 19).
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Wire wound
Gapped
Smooth
Threaded (a)
Mayer
(b)
5.21 (a) Mayer rod/bar (Ref. 19) (b) Mayer rod coater (adapted from Ref. 20).
Back-up roll
Doctor blade Applicator roll
5.22 Direct roll coating.
and is suitable for coating the undersurface of the substrate. The coating thickness depends on nip pressure, coating formulation, and absorbency of the web. Kiss coating A typical arrangement of kiss coating is shown in Fig. 5.23. The pick-up roll picks up coating material from the pan and is premetered by the applicator
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Application roll
Pick-up roll
5.23 Kiss coating.
roll. The coating is applied on the web as it kisses the applicator roll. The pick-up roll may be rubber covered, and the applicator roll may be made of steel. The metering is carried out by nip pressure, and consequently the amount of material coated on the web is dependent on nip pressure, speed of operation, roll hardness, and its finish. The coating weight and splitting of the film as it leaves the roll are also dependent on web tension. Gravure coating The gravure coating process relies on an engraved roller running in a coating bath, which fills the engraved dots or lines of the roller with the coating material. The excess coating on the roller is wiped off by the doctor blade and the coating is then deposited onto the substrate as it passes between the engraved roller and a pressure roller (Fig. 5.24).19 Reverse roll coating In this procedure, the coating material is measured onto the applicator roller by precision setting of the gap between the upper metering roller and the application roller below it. The coating is ‘wiped’ off the application roller by the substrate as it passes around the support roller at the bottom. Figure 5.25 illustrates a three-roll reverse roll coating process, although four-roll versions are common.19
5.7.4 Impregnators In the simple process of immersion (dip) coating, the substrate is dipped into a bath of the coating, which is normally of a low viscosity to enable
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Pressure roller
Doctor blade
Engraved roller
5.24 Gravure coating (adapted from Ref. 19). Doctor blade Metering roller Application roller
Support roller
5.25 Reverse roll coating (adapted from Ref. 19).
the coating to run back into the bath as the substrate emerges. This process is frequently used on porous substrates (Fig. 5.26).19
5.7.5 Hot-melt coating Extrusion coating/laminating Extrusion coating is the coating of a molten web of resin onto a substrate material. A typical extrusion-coating process is illustrated in Fig. 5.27.21 The
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5.26 Immersion/dip coating.
1
2
3 5 4
Substrate let-off
3
Wind-up
5.27 Extrusion coating: 1 extruder, 2 die, 3 chill rollers, 4 pressure roll, 5 slitter.
process involves an extruder which converts solid thermoplastic polymers into a melt/resin at the appropriate temperature required for coating, and this melt is extruded from a slot die at temperatures up to 320°C directly onto the moving substrate which is then passed through a nip consisting of a rubber-covered pressure roller and a chrome-plated cooling roll. The latter cools the molten film back into the solid state. The coated film is then slit by the micro-slitter to the desired size and then wound on the wind-up roller. Cross-head extrusion22 Another method of yarn coating is cross-head extrusion. In this process the flow of plastic is typically altered for permitting solid material, like fibreglass strands or metallic yarn, to feed into the melt flow, and thus become a part of the extrusion. Cross-head extrusion is usually used when reinforcements are not able to pass through the machine’s barrel and screw (Fig. 5.28).
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Core yarn
Coated yarn
5.28 Cross-head extrusion. Oven
Nip roll Slitter Chill roll
Primary substrate
Laminated film yarn
Secondary substrate
Adhesive deck
5.29 Adhesive laminating process (adapted from Ref. 21).
5.7.6 Laminating A laminated yarn can be produced by either an extrusion laminating process or an adhesive laminating process. Extrusion laminating is entirely the same process as ‘extrusion coating’, as shown in Fig. 5.27, except that the extruded hot molten resin acts as the bonding medium to a second web of material. Co-extrusion is again the same process only with two or more extruders coupled to a single die head in which the individually extruded melts are brought together and finally extruded as a multi-layer film.23 A typical adhesive laminating process is shown in Fig. 5.29 where two substrates are attached by an adhesive. The laminated material is then slit by a slitter before winding.
5.8
Applications and properties of some coated yarns
As mentioned earlier, there are numerous types of coated yarns due to the many kinds of coating substrate and coating materials (polymers). This
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section describes the application and properties of some useful and novel coated yarns.
5.8.1 PTFE-coated yarns24 PTFE-coated fibreglass yarns can be used in high heat and flame retardant applications. They are unaffected by rot, fungus and fuels. They exhibit excellent abrasion resistance and knot strength, increased flex life and reduced glass fibre fray. These PTFE-coated fibreglass yarns are used in wires and cables for aerospace applications, belting, and cable core fill material. Industrial applications of these yarns include release material, protective curtains and conveyor belts, e.g. in food processing machines. PTFE-coated kevlar and kevlar/stainless steel sewing thread from continuous filament kevlar yarns (twisted together with fine stainless steel wire) results in one of the strongest high temperature sewing threads. The PTFE coating completely encapsulates the thread, enhancing resistance to build-up of contaminants. In addition, the smooth coating improves handling characteristics and reduces the tendency of uncoated kevlar thread to fray, abrade and clog sewing equipment. PTFE-coated quartz sewing thread from high purity, very fine, continuous filament, pure fused silica is among the strongest and most temperature and chemically resistant threads. The PTFE coating process completely encapsulates the thread, enhancing resistance to build-up of contaminants and repelling attack by most acids and alkalis. This sewing thread will not support combustion and will not burn.
5.8.2 Ionomer-coated yarns The ionomer-coated yarns such as nylon coated with phenolic resin possess properties making them uniquely suited for mesh fabric bases for wet press felts. The outstanding adhesion of the coated yarns at the crossover points yields fabrics of exceptional stability.25
5.8.3 Adhesive-coated yarns for reinforcement Yarns can be reinforced by coating them with thermoplastic polymeric materials. A wide range of yarns such as carbon, aramid and glass yarn can be impregnated with thermoplastic PP, PA, PE, PET and other matrices. The yarns produced in this way have high shock resistance, a smooth surface and good reversibility. The latter property represents a substantial improvement from environmental and recycling aspects.26 Hot-melt coated filaments are a unique combination of adhesive and fibre reinforcement that are customized to meet exacting application requirements.
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Through proper selection of resin, coating level and fibre, a coated yarn can be optimized for adhesion and reinforcement properties. Adhesive-coated hot-melt yarns27 can be of the following types: ∑
Reinforced EVA adhesives: EVA is well known for its flexibility, toughness, adhesion characteristics and stress-crack resistance. It is commonly used for packaging reinforcements, composite preforms and roofing substrate selvages (Fig. 5.30).28 ∑ Reinforced polyamide adhesives: Polyamide nylon types are often referred to as high performance hot melts and their adhesives are well known for their ability to adhere to many types of filaments. They have a relatively high and sharp melting point along with high shear resistance. These adhesives show excellent resistance to washing and dry-cleaning solvents. ∑ Reinforced polyester adhesives: Polyesters offer excellent adhesion, great wash resistance, and resistance to dry-cleaning solvents. Reinforced polyester adhesives also offer excellent resistance to plasticizer migration, with high tensile strengths and fast set times. Thus are used over a broad spectrum of applications, including textile, footwear, industrial and product assembly applications.
5.8.4 Extrusion-coated yarns There is a wide range of material substrates and/or coatings for the manufacture of technical yarns for particular uses. Artificial fibre substrate may be aramid, carbon, fibreglass, high molecular weight polyethylene (HMPE), high modulus polypropylene (HMPP), liquid crystal polymers (LCP), nylon, polyester, etc. The resins used may be EVA, ionomers, nylon, polyester, polyethylene, polypropylene, polyurethane, polyvinylidene fluoride, PVC and many other resin systems. Some special extrusion coated yarns are as follows.
5.30 Packaging coated yarn products (Ref. 28).
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PVC-coated yarns PVC has long been recognized for its exceptional weathering performance, moisture resistance and abrasion resistance. PVC also provides abrasion resistance and a uniform surface for ease of braiding for protection of wire assemblies. PVC-coated nylon yarns may be designed for the braiding harness type constructions of electrical wiring systems.29 The vinyl coating is fire resistant and contributes sufficient fire retardancy to the yarn. The high-performance vinyl-coated nylon yarn performs at higher temperatures for extended periods of time while retaining the properties of high fire retardancy, abrasion and oil resistance. Vinyl-coated fibreglass yarn This type of yarn is used to weave insect screens that prevent the mosquitoes and other insects. The protective vinyl coating ensures lasting beauty, colour and flexibility. Moreover, it is non-combustible and will not rust, corrode or stain. It is well ventilated, well transparent, easy washing, anticorrosive and resistant to burning, has a strong tensile force, does not lose its shape, has a long service life and feels straight.30 Braid yarns designed for engineering applications are as follows:29 ∑
Thermoplastic polyester elastomer coating over high tenacity polyester multifilament. Especially designed for immersion in hydraulic fluid, while meeting a service temperature range of –50°F to 280°F (–45°C to 138°C). ∑ Polyurethane elastomer coating over nylon multifilament, for applications requiring increased flexibility and high surface friction with good abrasion resistance. ∑ Nylon 6,6 coating over high tenacity polyester multifilament. This yarn provides superior abrasion resistance, good heat stability and toughness. ∑ Polyvinylidene fluoride extruded over high tenacity polyester multifilament. Designed to meet very demanding conditions within engine valve covers, with a temperature tolerance of –65°F to 300°F (–54°C to 150°C).
5.8.5 Polymer-coated staple fibre yarns Not only artificial yarns but also cotton yarns are coated with a polymer solution to hold surface fibres to the yarn body, which cause fibre-fly generation during the knitting process.31
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5.8.6 Plasma-coated yarns Plasma-coated yarns have a wide field of application in medicine, and the properties of these yarns can be fully exploited in operating room clothing. When individual silver-coated yarns are woven into these textiles, this will create a dense fabric with antistatic and antimicrobial characteristics which will not let blood or secretions pass through. In addition, it will destroy germs and prevent electric charging. On the other hand, good conductivity is a desirable property in textile electrodes, which are created by embroidering using yarn that is coated with silver. As a result of their textile character, the electrodes may, for example, be integrated directly in a T-shirt and are therefore highly suitable for long-term electrocardiogram measurements. This enables heart diseases to be detected at an early stage.
5.8.7 Chitosan-coated yarns Antimicrobial textiles have been developed by coating chitosan over other cellulosic yarns such as cotton, and the antimicrobial action of such chitosancoated yarn was found to exhibit 100% activity. Such coated yarn is suitable for use in wound healing, antibiotic and antibacterial applications.32
5.8.8 Yarns coated with conductive substances An important aspect of using coated conductive yarns is in making intelligent and multifunctional fibrous materials. Metal-coated conductive yarns The need for flexible electrodes in garments and medical applications becomes more and more important. In this connection, textile fibres have been coated with precious metals such as gold, silver, platinum and palladium. The thickness, strong adhesion and surface coverage of the deposited precious metal layer, play a crucial role in the electroconductive and anticorrosion properties. Also such electrodes can resist a number of conditions such as washing cycles and contact with fluids such as urine or sweat and show excellent biocompatibility. CNT-coated conductive yarns In addition to the electrically conductive materials mentioned above, carbon nanotubes (CNT) have been found to be outstanding in coating synthetic and natural yarns such as 100% cotton yarn, silk yarn, wool/nylon mixed yarn, polyester yarn and polypropylene (PP) yarn. The substrate yarns were
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immersed in the prepared PVA/CNT solution and the CNTs bound by PVA were immobilized on the surface of the fibres, thus the yarns achieved electrical property.33 Currently, electronic smart textiles are made primarily of metallic or optical fibres. They are fragile and not comfortable. Metal fibres are also bulky, heavy and prone to corrosion. There are problems with washing such electronic textiles. On the other hand, intelligent textiles could monitor vital signs, warn of allergens, even cool off their wearers when the temperature rises. But wiring up fabrics with sensors has proved a challenge: most electronic textiles are too bulky to be worn comfortably and cannot perform sophisticated operations. Recently engineers at the University of Michigan have demonstrated a carbon nanotube-coated ‘smart yarn’. The threads can be woven into fabrics that are lightweight and wearable but act as simple, sensitive sensors that can, among other functions, detect human blood and monitor the health of the wearer. To make these ‘e-textiles’, they coated natural cotton threads with highly conductive, biosensing carbon nanotubes. These are regarded as among the most versatile nanomaterials available because of their mechanical strength and electrical properties. The researchers dispersed carbon nanotubes in a dilute solution of a mixture of Nafion, a commercial synthetic polymer, and ethanol. Then they repeatedly dipped cotton threads, 1.5 mm in diameter, into the solution, letting them dry between each dip. This allowed the nanotubes to cover individual cotton strands and to adhere strongly to the surface of the cellulose fibres in the strands. Since carbon nanotubes are conductive, after several dips the cotton threads became conductive enough even to be used as a wire to transmit a voltage to illuminate an LED light. They showed that a light-emitting diode (LED) put into a circuit between two of the coated cotton threads shines brightly (Fig. 5.31). The only perceptible change to the yarn is that it turned black, due to the carbon, but it remained pliable and soft. In order to put this conductivity to use, they added the antibody antialbumin to the carbon nanotube solution. Anti-albumin reacts with albumin, a protein found in blood. When the researchers exposed their anti-albumininfused smart yarn to albumin, they found that the conductivity significantly increased. Their new material is more sensitive and selective as well as simpler and more durable than other electronic textiles. This carbon-nanotube coated smart yarn can conduct enough electricity from a battery to power a light-emitting diode device. Researchers can use its conductivity to design garments that detect blood. The researchers claimed that this nanotube-coated cotton keeps the properties of the textile and adds new functions such as detecting blood. Such clothing that can detect blood could be useful in high-risk professions. An unconscious firefighter, an ambushed soldier, or a police officer in an
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(a)
(b)
5.31 Photographs of SWNT-coated cotton yarn: (a) comparison of the original and coated yarn; (b) 1 m long piece as made; (c) demonstration of LED emission with the current passing through the coated yarn (Ref. 34).
accident, for example, could not send a distress signal to a central command post, but the smart clothing would have this capability. The concept of electrically sensitive clothing made of carbon-nanotubecoated cotton is flexible in implementations and can be adapted for a variety of health monitoring tasks as well as high performance garments. It is conceivable that clothes made out of this material could be designed to harvest energy or store it, providing power for small electronic devices, but such developments are many years away and pose difficult challenges.34
5.9
Future trends
The expectations of consumers concerning the performance level of products, namely through multifunctional properties, are always increasing. Coating is the technology that can completely transform the appearance, handle, properties and performance of yarns as well as textiles. Consequently, its application has grown rapidly worldwide, especially since the emergence of various different revolutionary types of nanomaterials. Among the numerous categories in the evolving field of newly synthesized nanomaterials, carbon nanotubes (CNTs) are perhaps the most dynamic and are undergoing development at a rapid pace. The past five years have witnessed relentless growth in research, development and technological understanding of these remarkable materials. Universities, small businesses and start-ups, as well as large corporations, have continued to probe and exploit numerous commercial possibilities of high performance technical yarns by coating with CNTs. The list of product applications is expanding considerably and is projected to do so well into the future. Textile yarns with biosensing or sensing properties in general are also possible routes to the realization of highly desirable technical yarns, and
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are one of the most rapidly expanding sectors in the technical yarn market. Medical yarns are the products and constructions used for medical and biological applications and are used primarily for first aid, surgery, clinical and hygienic purposes. The main requirement of such textile materials is bioreceptivity and biocompatibility at the application site in human beings, e.g., for antimicrobial sutures. Today, silver has become the key ingredient in many forms of high-tech antimicrobial coated yarn. The use of silver for its functions in eliminating bacteria, mould, fungi and other microbes has greatly increased in providing antimicrobial coatings. Polymer collected from natural resources like chitosan has also been successfully coated in making antimicrobial yarns. In addition, mite-proof, insect-proof, odourless, flame-retardant, soilresistant, anti-UV and anti-electromagnetic radiation yarns have already been produced by coating. In the field of specialized applications of technical yarns, a huge amount of research is being conducted worldwide. Hence it is expected that with further development of technology and machinery, the technological assets of the new coated yarns are those that provide the highest performance and comfort standards, and ensure a better quality of life.
5.10
References
1. ‘Coated and laminated fabrics: Putting the industry in perspective’, available from http://www.intexa.com/downloads/coated.pdf [accessed 18 April 2009]. 2. Sen A K (2001), Coated Textiles, Principles and Applications, Westport, CT, Technomic Publishing. 3. Holme I (2003), ‘Coating and lamination enhance textile performance’, Technical Textiles International (TTI) available from htttp://findarticles.com/p/articles/ mi_qa5405/is_200309/ai_n21336901/?tag=content;col1 [accessed 18 April 2009]. 4. Hall M E (2000), ‘Coating of technical textiles’ in Horrocks A R and Anand S C, Handbook of Technical Textiles, Cambridge, UK, Woodhead, 173–186. 5. Kim B, Koncar V and Dufour C (2006), ‘Polyaniline-coated PET conductive yarns: Study of electrical, mechanical, and electro-mechanical properties’, J. Appl. Polym. Sci., 101, 1252–1256. 6. Available from http://en.wikipedia.org/wiki/Polyaniline [accessed 18 April 2009]. 7. Available from http://www.industrialrubbergoods.com/rubber-coating.html [accessed 15 April 2009]. 8. Available from http://www.industrialrubbergoods.com/ethylene-propylene-dienemonomer.html [accessed 2 March 2010]. 9. Available from http://en.wikipedia.org/wiki/Ethylene_vinyl_acetate [accessed 18 April 2009]. 10. Available from http://en.wikipedia.org/wiki/Chitosan [accessed 18 April 2009]. 11. Iijima S (1991), ‘Helical microtubules of graphitic carbon’, Nature, 354, 56–58. 12. Available from http://mrsec.wisc.edu/Edetc/nanoquest/carbon/index.html [accessed 15 April 2009]. 13. Available from http://www.pa.msu.edu/cmp/csc/ntproperties/ [accessed 12 April 2009].
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14. Available from http://www.evonet.be/~centex02/bigimages_2008/2009-2011_CNT_ II_Eng.pdf [accessed 12 April 2009]. 15. Available from http://www.techexchange.com/thelibrary/nanotechnology.html [accessed 12 April 2009]. 16. Schwarz A, Hakuzimana J, Gasana E, Westbroek P and Langenhove L V (2008), ‘Gold coated polyester yarn’, Adv. Sci. Tech., 60, 47–51. 17. Hegemann D (2007), Conference paper from the ‘NanoEurope Fair and Conference’, available from http://www.olma-messen.ch/wDeutsch/img/messen/nanoeurope/ Medienmitteilungen/Medienorientierung_Referat_HE_E_070910.pdf [accessed 13 April 2009]. 18. Available from http://www.spickglobal.com/laminated-films.html [accessed 10 April 2009]. 19. Available from: http://www.tciinc.com/coating.html [accessed 20 April 2009]. 20. Cohen E D (2005), ‘Mayer rod coater’, available from http://www.webcoatingblog. com/blog/2005/07/mayer_rod_coate.html [accessed 20 April 2009]. 21. Dodrill D (2008), ‘Advances in peelable sealant technology’, available from http:// www.rollprint.com/PDF/PeelableSealants.pdf [accessed 18 April 2009]. 22. Available from http://www.extrudedprofilesworld.com/cross-head-extrusion.html [accessed 18 April 2009]. 23. Available from http://en.wikipedia.org/wiki/Extrusion_coating [accessed 20 April 2009]. 24. Available from http://www.wflake.com/thread/ [accessed 18 April 2009]. 25. ‘Ionomer-coated yarns and their use in papermakers wet press felts’, US Patent 4520059, 28 May 1985. 26. Available from http://www.directindustry.com/prod/seal-spa/thermoplastic-prepregsystem-50483-342283.html [accessed 18 April 2009]. 27. Available from http://www.enyarns.com/adhesive.html [accessed 18 April 2009]. 28. Available from http://www.phifer.com/EngCoatedYarnProducts.aspx [accessed 18 April 2009]. 29. Available from http://www.enyarns.com/textilur.html) [accessed 18 April 2009]. 30. Available from http://www.jwfg.com/fibreglass-insect-screening/vinyl-coatedfibreglass-yarn.htm [accessed 18 April 2009]. 31. Koo Y S (2001), ‘Bending behavior of coated yarns’, Fibres and Polymers, 2, 148–152. 32. Shanmugasundaram O L (2006), ‘Chitosan coated cotton yarn and its effect on antimicrobial activity’, J. Text. Apparel Tech. Management, 5, 1–6. 33. Xue P, Park K H, Tao X M, Chen W, and Cheng X Y (2007), ‘Electrically conductive yarns based on PVA/carbon nanotubes’, Composite Structures, 78, 271–277. 34. Kotov N (2008), ‘Smart electronic yarns and wearable fabrics for human biomonitoring made by carbon nanotube coating with polyelectrolytes’, Nano Letters, 8, 4151– 4157.
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6
Engineering finer and softer textile yarns
J. S r i n i v a s a n, Kumaraguru College of Technology, India
Abstract: Use of finer and softer textile yarns will improve the aesthetics of fabrics and will be useful in producing highly fashionable materials. This chapter discusses the methods of engineering finer and softer textile yarns including raw material requirements, fibre to yarn conversion systems such as Sirospinning, Solospinning, compact spinning, jetring, jetwind, core, cover and wrap spinning, vortex spinning, twistless spinning, self twist spinning and air-jet texturing. Further, the details of structure including fibre distribution and packing density, aesthetic, comfort and other properties of these yarns, their applications and their future trends using bamboo fibres and microfibres are discussed. Key words: fine and soft textile yarns, engineering methods, structure and properties, applications and future trends.
6.1
Introduction: importance of finer and softer yarns
The use of finer and softer yarns gives a soft ‘hand’ to fabrics. A coarse fibre (i.e. one having a higher linear density) is stiffer than a fine one. Consequently fabrics made from coarse fibres often feel harsh and prickly. Thus, one can understand the drive to use fine fibres that give a softer ‘hand’ to fabrics.63 It is likely that wool and flax have been used to spin yarns in prehistoric times and these fibres have been spun into yarns much finer than today’s modern machinery can produce. Egyptian mummy cloth was discovered that had 540 threads per inch in the width of the cloth.24 Use of finer and softer yarns will improve the aesthetics of fabrics and will be useful in producing highly fashionable materials which have superior aesthetic and sensual factors such as appearance, colour, handle, softness, bulkiness and special texture. Highly aesthetic thin fabrics are used for women’s dresses and blouses whereas medium and thick fabrics are used for suits, skirts, slacks, formal wear, coats and sports/casual wear. Two aspects of wear comfort of clothing include thermophysiological wear comfort and skin sensorial wear comfort. Thermophysiological wear comfort is concerned with the heat and moisture transport properties of clothing and the way that clothing helps to maintain the heat balance of the body during various levels of activity. Skin sensorial wear comfort is concerned with the mechanical contact of the fabric with the skin, its 185 © Woodhead Publishing Limited, 2010
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softness and pliability in movement and its lack of prickle, irritation and cling when damp.23 Thermophysiological and sensorial properties, including liquid moisture transfer properties assessed for heat-resistant materials with different fibre contents, yarn properties, weave types and functional finishes in varying conditions of physical activity and environment, show that softer yarns with finer fibres produce measurably smoother fabrics with small contact.72 Thermal absorptivity is a transient phenomenon of heat flow reflecting the fact that the ‘warm–cool feeling’ effect of fabrics depends on the smoothness or roughness of the fabric surface. Fabrics with smooth surfaces have higher thermal absorptivity values as they provide a large area of contact with human skin.69
6.2
Methods of engineering finer and softer yarns
Spun yarn is a yarn produced by spinning staple fibres into a continuous strand. Yarns can be made of continuous filaments, staple fibres or combinations thereof. Natural fibres can be classified into two categories: short staple fibres (cotton-like, with typical staple or filament length 15–60 mm) and long staple fibres (wool-like, typical staple length 40–200 mm). Synthetic fibres are first made as continuous filaments; they can be subsequently converted into staple fibres by either cutting or stretch-breaking processes. Staple fibres can be made into yarn by a process of pulling and twisting strands of parallel fibres, generally referred to as spinning. For this reason, yarn made from staple fibres is called spun yarn. Industrial yarn spinning processes include the basic process steps of loosening, carding, drawing and spinning. Loosening refers to separating and optionally cleaning of, for example, baled staple fibres. Carding is the further loosening and separating of fibres, for example by passing them between rotating drums covered with needles. This results in a thin web of partly parallel fibres, which is formed into a ropelike strand often called a sliver. Combing may then be applied to enhance the orientation of fibres and to remove short fibres. During drawing, slivers are drawn out in one or more steps. Several slivers, either of the same or of different staple fibres, may be blended together in order to obtain a uniform fibre density. Mixing staple fibres at the carding stage can also make yarns comprising blends of different natural and/or synthetic fibres. Before feeding to the spinning machine, the sliver may be further drawn while a slight twist is added, resulting in a product called roving. During spinning, the sliver or roving is further drawn out and a twist is added to provide cohesion of the overlapping fibres, and the yarn is wound onto bobbins. Such a package of wound yarn may be of conical or cylindrical form, and is normally simply referred to as package.
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6.2.1 Raw material requirements for engineering finer and softer yarns To make fine, lightweight summer wear from wool, it is important to choose the correct wools and the right spinning and weaving technologies. The main factors that need to be selected to produce fine yarns and lightweight garments are28 ∑ Fibre diameter ∑ Fibre length ∑ Fibre modification ∑ Spinning technology. The secret of making wool fabrics to be warm is to engineer the bulk of the yarns (bulky yarns trap air that acts as an insulator and leads to warmth) and to produce hairy yarns and fabrics (hairy yarns trap air, and reduce direct contact of the skin with the fabric). In contrast, cool fabrics are made from fine, lean yarns and the fabric surface is kept as light and as smooth as possible. This encourages the fabric to have direct contact with the skin so that wool’s unique moisture and heat transfer characteristics, and its ability to ‘breathe’, can produce maximum cooling benefits. Human skin is extremely sensitive to even transient heating and cooling sensations. As warm skin closely approaches a wool fabric, the heat of the skin drives moisture from the surface of the fabric, and the fabric cools slightly. This is easily detected by the skin, and smooth lean wool fabrics will invariably feel cooler to the touch than other fabrics. Fibre diameter Fibre diameter is perhaps the most important determinant when producing lightweight wool fabrics. It is the diameter of the wool fibre that gives lightweight garments the qualities consumers are looking for. The finer the fibre, the softer and lighter the fabric. Furthermore, fibre diameter affects fabric handle, appearance and comfort. Fine Australian wools are comfortable and suitable for next-to-skin wear. Using wools with fibre diameters less than 18 microns gives garment designers a range of lightweight, next-to-skin wear options from lingerie to active sports wear to outer wear. Table 6.1 shows how fabrics with a range of stiffness can be produced by appropriate selection of yarn diameter, crimp (curvature) and, importantly, fibre diameter (micron), for a given fabric weight and construction. The coolest, softest fabrics will be produced from the finest, lowest crimped fibres.
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Table 6.1 Selection of fibre diameter and crimp for cooler, softer fabrics Diameter
18 mm
19 mm
21 mm
23 mm
Curvature type
Low High Low High Low High Low High
Plain weave sett at 56/48 ends/picks 209 211 205 207 202 205 194 206 per inch, top dyed fabric weight (g/m2) Stiffness index –1.2 –0.7 0.3 –0.7 1.2 2.2 2.5 3.9 Gabardine weave sett at 88/52 (84/46) ends/picks per inch, top dyed fabric weight (g/m2) Stiffness index
209 208 201 209
–5.3 –5.2 –4.5 –4.2
206 207 207 215
0
0.1 –0.4 –1.0
Plain weave sett at 56/48 ends/picks 217 226 216 220 214 214 201 211 per inch, piece dyed fabric weight (g/m2) Stiffness index –1.9 –0.9 –1.3 –1.5 0.5 1.2 1.8 3.4 Gabardine weave sett at 88/52 (84/46) ends/picks per inch, piece dyed fabric weight (g/m2) Stiffness index
215 216 210 220
211 210 208 218
–5.6 –5.4 –4.8 –4.0 –1.9 –1.6 –0.8 –0.3
Source: Ref. 28. Table 6.2 Effect of hauteur on yarn evenness and spinning performance Hauteur, mm CV% (evenness) Ends-down/1000 sp.hr.
50 21.1 228
60 20.7 92
70 20.4 49
80 20.0 29
90 19.7 19
Source: Ref. 28.
Fibre length Research at CSIRO Textile and Fibre Technology, Australia, has shown that the longer the fibre the better will be the properties of the yarns. An increase in fibre length in the top can result in finer and more even yarns, i.e. the ability to spin with fewer fibres in the cross-section. It also leads to yarns with less fibre hairiness, and fabrics with less surface hairiness, and as a by-product, fewer breaks in spinning (Table 6.2). Fibre modification Optim™ is one of the most exciting technical advances for years, moving the global textile industry a step closer to realising the full potential of wool, and is the first fundamental alteration to wool fibre in the history of fibre processing.20 It repositions wool into new market areas that satisfy customer demand for lightweight quality and trans-seasonal innovation. It is
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a new state-of-the-art fibre technology process developed by The Woolmark Company and CSIRO Textile and Fibre Technology. Invetech has taken the prototype process and designed the machine for commercial manufacture and operation. The Optim™ Wool Fibre Processing Machine is an automated, unmanned process line capable of producing 40 kg of fibre per hour. The Optim™ process can produce two quite different supreme luxury fibres each with a series of properties and characteristics that uniquely identify them apart from other natural fibres. Optim™ Fine has ultra-fine fibres with a structure and physical properties that closely resemble silk, providing weavers and knitters the scope to create high quality, sophisticated, lightweight fabrics that are soft to handle. Fabrics made from Optim™ Fine fibres have a silklike touch, fluid drape, distinctive sheen and subtle lustre, plus the natural performance benefits of wool. Optim™ Max is a unique fibre with latent retraction potential, designed to develop volume and bulk in wool yarns. Following blending with untreated wool, the Optim™ Max fibre is allowed to contract during wet processing. This produces a revolutionary new yarn which is less dense and has greater covering power than an equivalent conventional yarn and is ideally suited to the manufacture of lightweight garments, particularly knitwear. In lightweight knitwear production, Optim™ Max blended yarn takes up more space, so less yarn is required per square metre compared with the equivalent in regular pure new wool. The Optim™ wool fibre processing machine uses a series of chemical, heat and mechanical processes to achieve a 3–4 micron reduction in wool fibre diameter. This adds considerable commercial value to the fibre, and enables new fabric developments and applications.
6.2.2 Fibre to yarn conversion systems Woollen and worsted spinning The common spinning systems available for conversion of staple fibres into yarns are the cotton system, the worsted system and the woollen system. Depending on the spinning method used, yarn produced by the wool manufacturing industry is classified into woollen, fine worsted, coarse worsted and semi-worsted yarn and depending on the materials used into pure wool and blended wool.88 The woollen system is normally used for coarse wool and reclaimed fibres, artificial fibres (50–80 mm) and waste fibres. This system produces yarn which has high bulk but low strength. On the other hand, the worsted system, which involves many passages of gill drawing and combing, produces strong and compact yarn. The worsted system can utilise long and medium length wool and artificial fibres of 70–140 mm length. Woollen yarns are used for light dress materials, carpets, cords and serges, felts, blankets, rugs, fur for trimmings, etc. Worsted yarns are used for making
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dress materials, shawls, very fine clothes, lustrous worsteds, braids, fabrics with raised face, etc. Another system known as the semi-worsted system which dispenses with combing of wool is also used for certain purposes. The Sirospun process Sirospun is especially suited to the production of lightweight trans-seasonal cool wool fabrics (Fig. 6.1). Yarns produced by the Sirospun spinning process are fine, even and less hairy than conventional yarns. The fabrics produced from these yarns have a smooth feel that gives a cool feeling to the Sirospun fabric. Fabrics made from Sirospun wool yarns are well suited to the ‘cool wool’ concept and have been promoted throughout the world. Figure 6.2
Roving guide
Rear roller
Predrafting zone condenser
Midddle roller Apron
Main drafting zone condenser Front roller
Yarn break detector
6.1 The Sirospun process for the worsted ring spinning machine28 (courtesy: CSIRO, Australia).
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6.2 Sirospun attachment in place28 (courtesy: CSIRO, Australia).
provides an image of the grooved rollers attachment used to convert a conventional spinning frame to produce Sirospun yarns. The grooves in the ancillary rollers wrap the fibre ends into the yarn structure and produce a smoother and cooler yarn. Solospun Solospinning and compact spinning are essentially modifications to the conventional ring spinning process with the aim of altering the geometry of the spinning triangle to improve the structure of the ring spun yarn by effective binding of surface fibres into the yarn. The difference between these principles of solo and compact spinning is shown in Fig. 6.3. Solospinning makes single worsted/semi-worsted yarns suitable for use as warp in weaving, dispensing with ply twisting.24 Solospinning allows the use of finer yarns for lighter-weight fabrics, opening up new possibilities in product design. Spun from a single roving, Solospun yarns can be knitted or woven directly without the need for two-folding, resulting in lighter-weight, softer fabrics. Normally, spinning efficiency requirements prevent the spinning of conventional worsted single yarns with fewer than 35 to 40 fibres in the cross-section. Two-fold yarns therefore normally have averages of at least 70 to 80 total fibres. Solospun’s mean fibre limit of 60 to 65 is therefore a significant improvement over conventional
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Conventional Nip line
Solo
Edge fibres
To ring and traveller
Ts
Compact
Wy
Ts
Ts
W1
W2
Ts
6.3 Solo and compact spinning principles.24
two-fold yarns in terms of the fibre diameter required to efficiently spin and process a given yarn count. This can lead to lightweight cool fabrics. Even lighter-weight, all-wool fabrics can successfully be produced from Solospun yarns with resultant fibre numbers in the cross-section of less than 60 or 65 fibres. This is achieved by blending wool with water-soluble, modified PVA fibres prior to spinning, so that the total fibre number is at or above the minimum required, thus ensuring that the spinning and weaving performance is within acceptable limits. Dissolving the PVA fibres during the fabric finishing routine results in all-wool yarns with less than 60 fibres in the cross-section, giving rise to even softer and lighter fabrics. Compact spinning In compact spinning (also called condensed spinning), the fibres leaving the front roller nip are tightly compacted. The compact spinning concept, as embodied in Rieter’s COM4 yarns and Suessen’s Elite yarns, has been well publicised in recent years. For both types of compact spun yarn, the major advantage over conventional ring spun yarns is the much reduced yarn hairiness. This is achieved by modifications to the drafting process of conventional ring spinning. The advent of these compact spun systems also highlights the importance of yarn hairiness as a key factor affecting the yarn and fabric processes and properties. The characteristics of yarn hairiness have been discussed in detail.21
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Recently different ways of modifying existing spinning and winding systems to achieve improved yarn properties have been tried. These modifications are discussed below in separate sections on JetRing, JetWind and JetWind Plus. While the first two approaches can reduce yarn hairiness significantly, the third one has the additional advantage of engineering very fine and soft yarns from existing yarns produced on any staple spinning system.87 The JetRing process The JetRing spinning system is essentially a modified ring spinning system. The difference is that in JetRing spinning, a single air-jet is employed below the spinning triangle of a conventional spinning system as shown in Fig. 6.4.84 Therefore, JetRing spinning also has features of an air-jet spinning system. The idea is to make a yarn that is as strong as a conventional ring spun yarn, but considerably less hairy. When in operation, the jet twists the yarn in a reverse direction as does the first jet in air-jet spinning. But, unlike air-jet spinning, the single jet here induces an upward swirling airflow against the yarn movement. This arrangement was meant to facilitate piecing and reduce yarn hairiness efficiently. Barella21 and Pillay58 have found that most of the protruding fibre ends correspond to fibre tails for ring spun yarns. Therefore, an airflow in the direction of yarn movement may promote, rather than suppress, these protruding fibre ends. Furthermore, since the swirling air currents in the jet twist the yarn strand in the reverse direction, the twist level in the strand immediately above the jet is lower than that in the strand below the jet. Therefore, as the fibre strand traverses through the jet, the strand structure first gets loosened to some extent and then tightens up again as the strand emerges from the jet. This loosening and tightening
Front rollers
Air jet Pigtail guide
Ring and traveller
Yarn bobbin
6.4 A schematic diagram of the JetRing spinning system.87
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up of the strand structure may facilitate the tucking of fibre ends into the body of the yarn, thus effectively reducing yarn hairiness. It is also worth noting that the air pressure inside the jet is higher than that outside the jet. Kalyanaraman47 has found that by increasing the pressure of air around the point of fibre twisting, the yarn hairiness can be significantly reduced. With the JetRing arrangement, it is expected that the combined effects of swirling air, reverse twisting and air pressure would lead to an effective reduction in yarn hairiness without jeopardising other important yarn properties. Manual yarn piecing is not a problem for the JetRing either. Once the starter yarn is offered to the lower end of the jet, the airflow will suck the yarn through the jet. The yarn can then be collected from the upper end of the jet to make the piecing as in conventional ring spinning. The JetWind process The JetWind process is a further development of the JetRing concept. Instead of attaching an air nozzle during ring spinning, the air-jet is used in conjunction with a yarn winding process (hence the name JetWind). In the context of hairiness reduction, the JetWind process is more attractive because of the high production rate of winding and the fact that winding itself increases yarn hairiness. Several attempts have been made in the past to reduce yarn hairiness during winding. Muratec’s hairiness reducing winder (No. 151 Perla) is a good example. It employs a pair of false twisting rollers to wrap surface fibres around the yarn to reduce yarn hairiness. Another method of reducing yarn hairiness in winding was due to the joint effort of the Institute of Textile Technology (ITT) and Murata.68 It was reported that the ITT/Murata method employed an air vortex nozzle in winding ‘to wrap the long-hair fibres around the body of the yarn’. An air-jet nozzle originally for use in air-jet spinning has been attached to a grooved drum winder to reduce yarn hairiness. The air-jet attachment is positioned about 2 cm in front of the Uster classimat sensor between the yarn tensioners on a Mettler type SPE grooved drum winder. The winder operates at a speed of 400 m/min. To eliminate unexpected sources of variation, only one winding position was used in this study, and no waxing was applied during yarn winding. The pressure of compressed air supplied to the jet nozzle was kept constant at 0.5 bar in this study.85 A package of rotor spun yarn (18.5 tex, combed cotton) was rewound first so that the direction of the majority of protruding fibre ends now becomes trailing, and the rewound package was then used for a second rewinding with and without the air-jet. As can be seen from Fig. 6.5(a), the direction of the air vortex serves to suppress the trailing fibre ends and lower the twist level before the yarn enters the jet. As with JetRing, this arrangement has been found to achieve a significant reduction in yarn hairiness. The relative hairiness
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Yarn traverse
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150 140 130 120 110 100 90 80 70 60 50 2nd normal wind Normal wind
(a)
(b)
2nd wind with jet
6.5 (a) Layout of experiment; (b) hairiness results.87
Coarse yarn in
Untwisting element Back drafting rollers (slower)
Finer yarn out
Front drafting rollers (faster)
6.6 The ‘drafting-against-untwisting’ concept to make a finer yarn.90
results in Fig. 6.5(b) indicate a significant drop in yarn hairiness when the air-jet was applied in this way. If the directions of majority of protruding fibre ends and the air vortex inside the air-jet are not as depicted in Fig. 6.5(a) the reduction in hairiness is not as large. The JetWind Plus process Recently, the JetWind concept was developed even further to incorporate a simultaneous untwisting and drafting in the process. This is called the JetWind Plus process. The objective is to engineer fine, soft and low-hairiness yarns. The simultaneous untwisting and drafting concept is depicted in Fig. 6.6.90 In this process, a coarse yarn is fed into a pair of drafting rollers, a ‘false’ untwisting element (e.g. air nozzle as shown in Fig. 6.7) temporarily removes the twist in the yarn to facilitate drafting or attenuation, and the twist automatically returns to the attenuated yarn at the exit of the untwisting element. This would give a much finer and softer yarn than the ‘parent’ feed yarn. The fineness comes from the attenuation, and the softness comes from the reduced twist level per unit length, because the original twist is redistributed over a longer length of yarn.
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Wrapped fibres Air-jet orifice angle (a°)
Lmm Compressed air inlet
Air chamber
Protruding fibres
a° Untwisting zone
6.7 The air nozzle.
Dmm
90
With this process, since yarn is made finer after spinning, a relatively coarse yarn can be produced first in spinning. This way, the yarn breakage rate will be significantly reduced in spinning and the yarn can be produced at a higher production rate and efficiency. Attenuating or drafting will improve the fibre alignment along the yarn axis, which in turn helps to improve the tenacity of the drafted fine yarn. The concept should apply to different types of yarns (worsted yarn, woollen yarn, rotor spun yarn, etc.). Since the original twist in the yarn will be distributed over a longer length after the ‘drafting-against-untwisting’ process, the overall twist level in the drafted yarn will be lower and the yarn will be softer than its ‘parent’ yarn. This should improve the softness of the fabric made from such a yarn. It is well known that twist in a yarn tends to accumulate in thin spots. Since a small amount of twist is kept in the yarn after partial untwisting, the ‘draftingagainst-untwisting’ process may preferentially draft the thick places more than the thin places, hence improving the evenness potential of the yarn. This concept can be incorporated into a normal winding process to achieve the hairiness reduction as in the JetWind process. In summary, the ‘drafting-against-untwisting’ process has the potential of producing stronger (in tenacity), more even (in irregularity index) and less hairy yarns than the existing technology. Experiments have been conducted on a prototype rig with woollen yarns, and the results are very encouraging. The test results for cashmere yarns are shown in Table 6.3. It can be seen that the yarn count was reduced by a factor of about 1.24, which is close to the nominal draft of 1.26 used for the experiment. The difference can
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Table 6.3 Properties of cashmere yarns before and after engineering Property
Parent yarn
Modified yarn
Spool 1
Spool 2
Spool 1
Yarn count (tex) Twist (t/m) Tenacity (cN/tex) Elongation (%)
56.1 735 2.65 19.67
56.2 732 2.70 20.41
45.2 605 2.60 10.49
Change ratio
Spool 2
Change ratio
1.24 1.21 1.01 1.87
45.7 605 2.64 11.70
1.23 1.20 1.02 1.74
(t/m) = turns per metre Source: Ref. 90.
be attributed to the well-known elastic behaviour of fibres during drafting6 coupled with some yarn elongation in the drafting zone due to untwisting. As expected, there was a reduction in twist level and the yarn also felt much softer after its modification. The tenacity of modified yarns remains more or less the same. Further work is on-going with other types of yarns, including worsted ring spun yarns and rotor spun yarns. Core, cover and wrap spinning Core spun yarn can be defined as a yarn consisting of a filament surrounded by staple fibres. Core spun yarns can be manufactured with staple fibres at the core as well as at the sheath. Core spun yarns can be manufactured by different methods such as ring spinning, open end spinning, air-jet spinning and friction spinning, and they find applications in industrial clothing and sewing threads.50 Cover spun and wrap spun yarns have been produced to enhance the strength and elongation properties of fine, soft, bulky, novelty and fancy yarns. Critical settings and their effects on the properties of openend cover spun yarns produced by a novel system are explained.48 The yarns are constructed from open-end rotor spun (OER) yarns and textured polyester yarns combined within the yarn formation zone of the rotor during the openend rotor spinning process. The end result is a textured yarn wrapped as a sheath around an OER yarn core, in which the distribution of wraps per metre is uniform, the yarn remains soft, and tensile properties are better than for an equivalent OER yarn. Wrap spinning is a yarn formation process in which a twistless staple fibre strand is wrapped by a continuous binder. The process is carried out on a hollow spindle machine. A variety of binders can be used to complement the staple core or to introduce special yarn features. Wrap spinning is highly productive and suitable for a wide range of yarn linear densities. Because the staple core is composed of parallel fibres with no twist, the yarn has a high bulk, good cover and very low hairiness.19 A hollow spindle/ring twisting machine for the simple and economical production of
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fine, soft, voluminous and balanced continuous and controlled thread and spinning effects has been demonstrated.33 To produce fashionable fancy twists that also satisfy the demand for maximum economic efficiency, Saurer Allma has developed the Fancynator. With its broad yarn count spectrum, the Fancynator is particularly versatile and offers an economical solution for large batches too, with up to 192 spindles. If flexibility and special effects are especially in demand, the Saurer Fashionator is the ideal machine. Simple programming of the effects makes lot changing easy. The plied yarns are also wound directly onto packages, a performance feature exclusive to the Fashionator that makes time-consuming, cost-intensive rewinding unnecessary. This makes the Fashionator particularly economical for smaller lots too. The Saurer Fancynator and Fashionator are best suited for use in machine knitting, clothing, furnishing fabrics, curtains and many more.36,70 Vortex spinning First introduced in 1997, Murata Vortex Spinning (MVS) has made rapid progress into short staple cotton and cotton-blend yarn markets for both knitting and weaving end-uses. Cotton and cotton-blend MVS yarns typically have a smooth, low hair finish and are consequently low-pilling. Fabrics produced using MVS have distinct physical advantages over other short staple and worsted yarns. MVS yarns have good abrasion and pilling resistance. Their smooth handle differentiates them from yarns spun on other systems. These characteristics make them highly suitable for a range of knitted or woven fabrics such as those used for interior textiles or lightweight blankets or next-to-skin apparel.55, 75 Twistless spinning The direct production of zero-twist staple yarn has the attraction that it overcomes the limitations imposed by the ring spinning system on the production rate, power consumption and package density. Because delivery speeds are independent of yarn count, twistless spinning may be particularly attractive for fine count spinning. According to TNO, the Netherlands, the developer of the original TNO system of twistless spinning for cotton, these yarns are cheaper than OE yarn for counts finer than about 15 to 20 tex.32 It is a continuous process for the spinning of twistless yarn from staple fibres in which sliver or roving containing not more than 80% by weight, based on the weight of fibre, of a liquid containing a dispersed potential binding agent is drafted. The potential binding agent, which may be starch, a starch derivative or a synthetic polymer dispersion, may be rendered adhesive by dielectric heat, radiant heat, heated vapour or polymerisation or by breaking
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labile crosslinks. The size of the particles of the potential binding agent is preferably not greater than the average fibre diameter.73 TNO is a twist-free spinning method. During the process a roving is wetted, drawn out, sprayed with size, then wound on a package; the fibres are steamed to bond together. Even though the yarns lack strength, the pressure between the warp and the filling can provide strength to them. Since the twist is eliminated, the yarn has a soft hand feel, and if the sizing is removed it is more lustrous. As the yarns are twistless they have good dyeability and durability. A similar fabric construction can be achieved by using wrap spun yarns which have been produced with a soluble binder. Open-end, twistless and ring yarns made from cotton and spun to different twists were knitted into single-jersey fabrics to assess their performance. Twistless yarns gave good fabric hand, high lustre, zero spirality and little shrinkage, but there was some loss in strength for the fabric tested.62 Self-twist spinning During the self-twist spinning process, there are two rollers which draw out two strands of roving and add twist to it. The twist direction may be either Z or S. Intermeshing and entanglement are achieved when two twisted yarns are brought together. The yarns may ply over each other after release of the pressure. Filament plies, staple plies or staple and filament plies may be combined by this method. The Repco self-twist system was initially intended for the production of two-fold worsted weaving yarns, but it has since been developed further.32 The Platt type 888 self-twist spinner produces a twoply yarn without employing spindles, rings or travellers, thus eliminating completely the limiting factors to productivity of ring spinning. Spinning tension – often very high on ring frames – is replaced by much lower, controlled winding tension; reducing spinning end breaks and virtually eliminating the emission of fly and dust at the spinning operation. Delivery speed is normally 220 metres per minute, irrespective of the yarn count produced. This delivery speed is approximately 12 times greater than that of a ring frame spinning fine count yarn. In addition, the machine produces a two-fold yarn directly at the spinning operation, each winding unit representing the productivity equivalent of 24 ring spindles.59
6.2.3 Air-jet texturing In general, various methods of texturing require that the yarns be thermoplastic so that they can be heat set. This precludes the use of non-thermoplastic yarns like rayon. Air-jet texturing provides a means of creating texture in such materials. Further, it is a useful means of producing a yarn structure near to that associated with staple yarns. This is an important concession to
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the tastes of the ultimate consumer.63 Air-jet texturing was introduced by DuPont in the 1950s, and then was known as the Taslan® process. Recently, in air texturing the speed of processing can reach more than 900 metres per minute in certain cases. Figure 6.8 shows the basic principle of the process. The filaments or yarns are wetted, in order to improve process stability by reducing filament to filament or fibre to fibre friction, and fed into the texturing jet. Then, high pressure air or steam that accelerates to supersonic speeds is blasted on the material and this forces the filaments or fibres to buckle and mutually entrap each other in the turbulent airstream. These air jets are enclosed in a ‘jet box’ which reduces the noise and collects water and spin finish as it is washed off the yarns. Heaters are further frequently used to remove the water remaining at the end of the process and to set the bulk of the finished yarn. Because the filaments buckle and loop during the texturing process, they need to be overfed as compared to the final delivery speed. It is possible to use air-jet texturing to combine two or more threadlines, which may vary in several ways and be fed at differing speeds. This allows the resultant yarn to be ‘engineered’ in terms of both its composition and its properties, and it opens the way for the production of what appear to be ‘fancy yarns’. The yarn created by this process is becoming more frequently used in apparel fabrics as developments in the feedstock and precise texturing techniques result in yarns that are becoming comfortable in wear. These new air-jet textured yarns are beginning to be used for knitted fabrics, and indeed are even used in fabrics for intimate apparel. All air-textured yarns have a reduced tensile strength compared with an untextured yarn because of the confusion of filaments or fibres. Fancy yarns, primarily slubs and boucles, can be made and, if the feeder yarns are chosen carefully, can be very successful. The very high speeds available in air-jet texturing (especially in comparison with conventional fancy twisting) offer sufficient commercial incentive to encourage research in producing a range of fancy effects by this means. In addition, work involving new filament/fibre profiles and new
Compressed air
Yarn feed Yarn delivery
6.8 A continuous filament yarn being air-jet textured.35
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production techniques will allow more and more variety to be introduced into the yarns created by this process.67 Air-jet texturing can be used to engineer finer and softer textile yarns because of the flexibility and versatility of the process. Over the past two decades, a multitude of research work on air-jet texturing has been carried out on jet design, process and product development. These include efforts on air texturing spun cotton yarns,9, 13, 14, 41, 42, 82 processing and characterisation of blended/hybrid yarns and their fabrics8, 10, 11, 15–17, 35, 40, 49, 64, 65, 80 and the mechanism of the air-jet texturing process.1–5, 12, 22
6.3
Structure of fine yarns
A comparative study of the physical properties of cotton yarns produced by using new, modified and conventional spinning methods has shown that the structural differences of each yarn type conferred different tensile, evenness and hairiness values, and the differences in the yarn structure were reflected in the fabric properties.89 Figure 6.9 shows a comparison of ring spun and JetRing spun yarns. It is obvious that the addition of the air jet has led to a large reduction in yarn hairiness.
(a)
(b)
6.9 Comparison of (a) conventional ring spun yarn and (b) JetRing spun yarn (56 tex, 100% wool).87
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6.3.1 Fibre distribution and packing density of fine yarns During textile spinning processes, the fibre stream is arranged to form a yarn in many different ways according to the spinning method, machine setting and initial geometry of the fibres in the sliver or roving. This leads to a spun yarn with different structures and mechanical properties. A tracer fibre technique is an effective way to study the fibre path in a fine yarn. Together with an image analysis algorithm, a large number of tracer fibres can be sampled and a better representation of the yarn structure can be obtained. The yarn cross-section analysis provides some further information on the yarn structure, for example the fibre packing density distribution in a yarn. A very important yarn parameter is related to the highly non-linear torsional and tensile properties of yarn, and the initial lateral compression modulus of fabric and hence the fabric handle. A number of studies have been published on the subject of fibre distribution through the cross-section of the yarns and their packing density.29, 30, 71 For instance, fibre distribution through the cross-sections of compact yarns and their packing density values have been investigated to provide a better understanding of the internal structures of compact yarns produced by different compact spinning systems, since there is no information available so far regarding their internal structure.30 The results of packing density analysis indicated that compact yarns had nearly 15–30% higher packing density than conventional ring spun yarns. Also, the packing density values of compact yarns produced by three different compact yarn spinning systems, namely Rieter K44, Suessen Elite and Zinser Air-Com-Tex700, revealed that there were no significant differences among these systems in terms of yarn packing density values. In general, finer and softer yarns may have a higher packing density and a better fibre distribution and migration depending upon the method of engineering them and various other factors during processing.
6.3.2 Number of fibres in the yarn cross-section Traditionally, there are only two basic ways of making a fine yarn on a staple spinning system.87 ∑
∑
Reduce the number of fibres in the yarn cross-section so that the yarn thickness reduces to make a fine yarn. But there is a limit to this approach, since ring spinning requires a minimum average number of about 40 fibres in the yarn cross-section while rotor spinning requires a minimum average number of about 90 fibres in the yarn cross-section. Below these limits, spinning has proved to be uneconomical. Using very fine fibres to spin the yarn, so that fine yarns can be produced without reducing the number of fibres in the yarn cross-section. This is
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a more attractive approach, but the production of fine wool is limited at present, and the fine fibres are expensive. For instance, the diameter of the bulk of Australian wool production is in the 22–24 mm range. A few years ago, a Victorian wool grower obtained over one million dollars for a bale of superfine wool of about 14 mm (over $10,000 per kg). Unlike synthetic fibres, it takes decades to reduce the overall fineness of natural fibres such as wool. Therefore, the above two options have their respective drawbacks. In addition, when manufacturing fine yarns using these traditional approaches, the machine speed often needs to be reduced and the yarn twist increased to reduce ends-down. This not only lowers the production rate, but also adversely affects the yarn characteristics such as softness.
6.4
Properties of fine yarns
The handle (hand) values can be measured objectively by Kawabata’s Evaluation System developed recently. The hand values are expressed by various factors such as ‘Koshi’ (stiffness), ‘Hari’ (spread and anti-drape), ‘Fukurami’ (fullness and softness), ‘Shari’ (crispness), ‘Kishimi’ (scroopy feeling), ‘Numeri’ (smoothness) and ‘Shinayakasa’ (flexibility with soft feeling). Fine yarn fabrics are generally lightweight, resilient and resistant to wrinkling, have a luxurious drape and body, retain shape, resist pilling and have a good handle. Also, they are relatively strong and durable in relation to other fabrics of similar weight. In a fine yarn fabric, many fibres can be packed together very tightly. The denseness results in other desirable properties. With many more fine fibres required to form a yarn, a greater fibre surface area results, making deeper, richer and brighter colours possible. Also, since fine yarns can be packed tightly together, fine fibres work well in wind resistance and water repellency. Yet, the spaces between the yarns are porous enough to breathe and wick body moisture away from the body. When comparing two similar fabrics, one made from a conventional fibre and one from a finer fibre, generally the finer fibre fabric will be more breathable and more comfortable to wear. Finer fibres seem to be less ‘clammy’ in warm weather than conventional synthetics. In a fine yarn, since fibre strands are so fine, heat penetrates more quickly than with thicker conventional fibres. As a result, fine yarn fabrics are more heat sensitive and will scorch or glaze if too much heat is applied or if it is applied for too long a period. Generally, fine yarn fabrics are wrinkle resistant, but if pressing is needed at home or by drycleaners, care should be taken to use lower temperatures. Fine fibres give a soft handle and therefore greater comfort. For garments worn next to the skin, the mean fibre diameter in the spun yarn should be less than 28 mm. This is not an exact limit but is referred to as the itch point or comfort limit, because people generally © Woodhead Publishing Limited, 2010
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experience discomfort if greater than 3–4% of the fibres in the yarn are coarser than this value.31, 57 The fibres of merino wool have diameters of 10–30 mm. As a result, the mean of a given mass can be from 15 to 25 mm. Merino wools are suitable for garments worn next to the skin. Blends of wool incorporating coarser fibres can be made to give an average diameter of 25 mm but the fineness range can be 15 to 45 mm. Thus, for comfort garments, both the mean micron value and the distribution should be as small as possible.24 Although wool fineness is always given as a diameter, strictly speaking, the cross-sectional shape of wool can vary greatly: some are nearly circular, and most have varying degrees of ovality or ellipticity. A suitable way of expressing the ellipticity is by the ratio of major to minor axis to give what may be called a contour figure (CF). Generally, fibres with CF less than 1.22 will process acceptably well.83
6.5
Applications
Cashmere fibre is cylindrical, soft and silken, more like wool than any other hair fibre. It has a very soft, silky finish and is very light in weight. The applications of such soft fibres and yarns are in products like scarves, shawls, sweaters, hats, underwear, apparel, socks, quilts, etc.77 There are various applications for fine and soft yarns in apparel, bedding, linen and home textiles, bath towelling, sports and active wear, intimate wear and socks, textile made ups. For instance, anti-bacterial and anti-odour yarns, air vortex yarns, quick dry and Spandex yarn products are used for hygiene and comfort, breathability, moisture management and uniform stretch comfort in sports and active wear. Medical textiles and biomaterials are a significant and increasingly important part of the technical textiles industry. They cover a huge range of applications, from diapers and surgical gowns to substrates for electronic sensoring of vital life signs, external use as wound care and internal use as implantables for biodegradable post-operative support systems. They can also be used in the replacement of body parts through tissue engineering by supplying the structure for the growth of new cells. Even the humble plaster has the potential to deliver a powerful healthcare effect through its specific skin care characteristics and controlled delivery of medications.76 Recent advances include the development of polylactic acid and polyglycolic acid fibres as structures for cell growth, temporary bioresorbable textile supports for growing human organic tissue, and the development of smart fibres – based on naturally occurring polymers and also on non-animal-based protein fibres and structures – for the treatment of wounds and ulcers. These are a few examples of the wide range of textile-based non-implantable and implantable products used in medicine and surgery. Fine, soft yarns find applications in the above fields in one way or the other. Fine and soft yarns find applications
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in a wide range of men’s and children’s inner wear, ladies’ inner wear such as slips and panties, men’s briefs and trunks, men’s and children’s vests, etc. High grade raw materials are used for their fabrication, and such garments are also well appreciated for factors such as their availability in varied sizes, colour combinations and designs. Soft, fine satin-weave fabric of Egyptian cotton is used industrially as a lining material.34
6.6
Future trends
6.6.1 Bamboo, the green fibre for fine yarns in future After gaining popularity as a green fibre, bamboo has found a place in significant fashion circles. However, questions are often raised concerning the textile chemicals applied to bamboo for making it usable as fibres for clothing and other textile products.79 The inherent antifungal and antibacterial properties of bamboo fabrics make them suitable for such clothing as underwear, T-shirts and socks. Bamboo is especially preferred for making summer clothing as it gives protection against UV rays and for being naturally cool. The softness, sheen and drapability of bamboo fabric make it suitable for fashion clothing and fashion accessories like scarves. As it has good absorption and is breathable, it can be used in making any type of garments, especially sportswear and inner wear. In fact, some manufacturers use a blend of 4% Lycra with bamboo to make sportswear. The softness of bamboo yarn also makes it ideal for making infant wear. Bamboo fabric has also come to occupy an important place in the manufacture of home furnishings due to its many qualities, including softness, strength and durability among others. It is used in making cushion covers, table linen, bed linen, curtains, beddings and pillows, kitchen linen, wall papers and curtains, upholstery, etc. Bamboo fabric is increasingly being used in making bathroom furnishings. Bamboo bath towels and bath robes have a soft and comfortable feel and excellent moisture absorption capability. The natural antibiotic property of bamboo fabrics provides hygienic conditions as well as preventing bad odour. They are also suitable for making bath mats due to their good absorbency. Bamboo pulp is also used for making non-woven fabrics that are then used in making hygiene products such as sanitary napkins, masks, mattresses, absorbent pads and food-packing bags. Apart from non-wovens, bamboo fabric itself is also used in the production of such items as textiles for surgical practices including masks, bandages, gowns, etc., as well as linens, towels and drapes in hospitals.
6.6.2 Microfibre yarns Microfibres are extra-fine fibres with incredible fineness which changes the properties of the regular-sized fibres and gives them a wonderful hand and © Woodhead Publishing Limited, 2010
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drape. In spinning, the multiple microscopic-sized filaments or fibres have more motion and allow the fibres to shift lightly in the spun yarns for more drape and a very soft feel to prevent loss of their yarn structure. The resulting knits do not sag or droop. They also absorb and wick moisture better and seem to breathe. Microfibre knits feel more like natural fibres and feel less ‘clammy’ in warm weather than regular synthetic yarns.86 Compared with familiar fibres, microfibres are half the diameter of a fine silk fibre, one-third the diameter of cotton, a quarter the diameter of fine wool, and 100 times finer than human hair. This superfine quality means the softest feel against the skin. One warning about microfibres is that they are more heat sensitive than normal diameter fibres because they are so fine and the heat penetrates more quickly. They should not be pressed with a hot iron and they should not go into a hot clothes dryer. Microfibres are usually made of polyester, polyamide, acrylic, modal, lyocell or viscose in the range of 0.5–1.2 dtex. Properties of microfibres affecting the downstream process in mechanical processing and in the processing of microfibres in the blow room, carding, draw frame, speed frame and ring frame are presented in Table 6.4. Alternative spinning technologies such as open-end, air-jet and compact spinning are dealt with. In fabric forming systems, weaving and knitting with microfibres are discussed in depth, highlighting research on such fabrics. High-speed weaving of microfibres is discussed with reference to three major technologies of projectile, rapier and air-jet weaving. Different uses of microfibres in terms of industrial, medical, apparel and miscellaneous applications are presented.74 Studies on knitted fabrics from polyester and viscose microdenier fibres have been undertaken.43–46 Table 6.4 summarises the superiority of the polyester microfibre yarn over the normal fibre yarn in terms of the tenacity (RKM), evenness (Um%), imperfections, work of rupture and hairiness. The better yarn tenacity and uniformity of microfibre yarns are due to the larger number of fibres in the yarn cross-section and better packing of fibres in the yarn structure, respectively. Lower production speeds for processing of microfibres, as generally followed in the industry, have contributed to a Table 6.4 Polyester microfibre yarn properties Properties
Microdenier
Normal denier
Elongation (%) Tenacity (RKM) Evenness (Um%) Thin places (-30%) Thick places (+50%) Neps (+140%) Hairiness (3 mm)
11.23 37.60 7.53 74 km–1 4 km–1 17 km–1 207.2
11.18 34.68 8.66 273 km–1 6 km–1 33 km–1 1344.2
Source: Ref. 46.
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significant reduction in imperfections in microfibre yarns. Microfibre yarns showed an appreciable reduction in hairiness values and have a low lintshedding propensity. These observations may be due to the higher flexibility of the microfibres, which enables retaining them in a coherent structure. The wicking behaviour of the polyester microfibre fabrics was found to be better than that of the normal denier fabric. The water drop absorbency, drying rate and total absorbency of the microfibre fabrics were found to be better than those of the normal denier fabrics. However, pilling resistance and abrasion resistance of the microfibre fabrics did not vary significantly compared with normal denier fabrics. The bursting strength of the microfibre fabric was slightly better than that of the normal denier fabric.46 Microfibre performance apparel has become a very popular alternative to cotton apparel for athletic wear, such as cycling jerseys, because the microfibre material wicks moisture away from the body, keeping the wearer cool and dry. For the same reason, coupled with the elasticity of microfibre fabric, it is commonly used for women’s undergarments. Fabrics made with microfibres are exceptionally soft and hold their shape well. When highquality microfibre is combined with the right knitting process, it creates an extremely effective cleaning material. Microfibre is unsuitable for some cleaning applications as it accumulates dust, debris and particles. Sensitive surfaces (such as all high-tech coated surfaces, e.g. CRT, LCD and plasma screens) can easily be damaged by a microfibre cloth if it has picked up grit or other abrasive particles during use. The cloth itself is generally safer to use on these surfaces than other cloths, particularly as it requires no cleaning fluid. One way to minimise the risk of damage to flat surfaces is to use a flat, non-rugged microfibre cloth, as these tend to be less prone to retaining grit. This material can hold up to seven times its weight in water. Microfibre products also have exceptional ability to absorb oils. Microfibre is also used to make tough, very soft to the touch materials for general clothing use, often used in skirts and jackets.52 Microfibres are also used by the military for more rapid drying of the wearer and less skin irritation due to moisture. The US military has since banned the wearing of most synthetic clothing due to melting and burn risk.60 Microfibre yarn has a unique structure that acts in a capillary manner and removes dirt so small that it is undetectable to the human eye. Dirt and soiling are removed from surfaces into the cloth. While traditional round fibres smear the dirt, the microfibre removes it. Microfibre cloths were originally created to clean high-precision lenses. The specially segmented fibres that make up a microfibre cloth were developed to do this without the need for chemicals and cleaning fluids, and yet still deliver the highest possible standard of cleaning. Today, microfibre is more widely used to deliver the same high standard of cleaning to many kinds of hard surfaces including glass, mirrors, ceramic tiles, basins, taps, stainless steel, melamine,
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etc. Microfibre cloths are manufactured to the highest standards, each fibre being split 16 times during manufacture. This is the highest level of splitting possible.54 Splitting at this level not only creates a cloth with a much greater surface area, giving the cloth a higher capacity to absorb moisture and dirt, but it also makes the fibres soft and supple to avoid damaging the surfaces being cleaned. These cloths benefit further from securely bound edges and sealed corners to ensure they can be washed and reused hundreds of times without any drop in performance. Microfibre materials such as PrimaLoft are used for thermal insulation as a replacement for down feather insulation in sleeping bags and outdoor equipment, due to their better retention of heat when damp or wet. 61 A lot of fibre and fabric structures or finishing parameters influence the functional properties of fabrics. In order to assess the thermal properties of conventional polyester and microfibre types of fabrics, the plate/fabric/plate method for conductivity or cool/warm feeling has been used. Fabrics made of microfibres show lower heat conductance and therefore higher thermal insulation properties. Microfibre fabrics exhibit a warmer feeling than conventional polyester fabrics depending on pressure, which may be due to the difference in the fibre and fabric surface in contact with the human skin.51 The use of microfibres gives much higher volume for the same weight which explains their particular advantages. Textiles made from them have very high thread density. This means they have a much higher number of air chambers and tiny pores, allowing the skin to breathe and the body to regulate temperature more easily. Sportswear from microfibres functions particularly well. It is breathable and at the same time provides reliable protection against wind and rain. Fashionable apparel in microfibres has a graceful flow and a silk-like feel and is extremely comfortable. Microfibre clothing is not wash sensitive, retaining its positive qualities after washing or cleaning.53 A new series of synthetic fine fibres has been developed that do not have the various deficiencies of melt-blown and micro-glass materials in filtration. They are spun at standard deniers and can be easily processed and split into micro-denier fibres on textile-based and wet-laid non-wovens processes. The fibres can be blended and processed with other fibres for product designs that meet customer needs. These fibres are based on spinning fibres of at least two dissimilar polymers and can be spun into either segment-splittable or dissolvable ‘islands-in-the-sea’ formats. The fibre diameters currently available are between 2 and 3 microns, with below 1 micron being targeted. The fibre segments can be electrostatically charged. These fibres bring value to applications where properties such as sound and temperature insulation, fluidholding capacity, softness, strength and durability, lustre, high surface area, barrier property enhancement and filtration performance are needed. 37 Figure 6.10 illustrates splittable fibres as the world knows them today.
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PET Nylon
6.10 Standard pie wedge fibre.38
The cross-section is commonly referred to as ‘pie wedge’ or ‘citrus’, and the wedges are alternately made of nylon and polyester. It is common for such a fibre to have 16 segments. The conventional purpose of making a fibre like this is to form a card web of typically 3 denier per filament fibres, and then pass the web under hydroentangling jets which simultaneously split the fibres into individual wedges and entangle the fibres to give the fabric strength and integrity. As a result, the fabric contains fibres down to 0.2 denier per filament, but most of the throughput and processing advantages of a 3 denier fibre are maintained.38
6.7
Sources of further information and advice
Tracing the stylistic and functional threads that unite clothing across time and cultures – as well as delving into the divergent styles and significant apparel – A to Z encyclopedias are the essential resource for exploring the relationship between culture and couture. A number of such encyclopedias are available, including the Encyclopedia of clothing and fashion,81 Fashion: The Collection of the Kyoto Costume Institute: A History from the 18th to the 20th century,7 The face of fashion: cultural studies in fashion,39 Oxford history of art: Fashion,25 etc. International trade commission reports related to fine, soft yarns are available in reports, summaries, studies and other publications of the United States International Trade Commission,66 Sew Any Fabric: A Quick Reference Guide to Fabrics from A to Z, 26 the journal Textile Asia,78 etc. Some of the directories for fine, soft yarns include The Yarn Book: textile Handbook: How to understand, design and use yarn,56 Sensual Crochet, Luxurious yarns, Alluring designs,18 The knitter’s book of yarn: the ultimate guide to choosing, using and enjoying yarn,27 etc.
6.8
References
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3. Acar M, Turton R K and Wray G R (1986), An analysis of the air-jet yarn texturing process, Part III: Filament behaviour during texturing, Journal of the Textile Institute, 77, 235–246. 4. Acar M, Turton R K and Wray G R (1986), An analysis of the air-jet yarn texturing process, Part IV: Fluid forces acting on the filaments and the effects of filaments cross-sectional area and shape, Journal of the Textile Institute, 77, 247–254. 5. Acar M, Bilgin S, Versteeg H K, Dani N and Oxenham W (2006), The mechanism of the air-jet texturing: The role of wetting, spin finish and friction in forming and fixing loops, Textile Research Journal, 76, 116–125. 6. El-Sharkawy A F and Audivert R (1974), The relation between the theoretical and the actual draft in the roller-drafting of staple-fibre slivers, Journal of the Textile Institute, 65, 449. 7. Fukai A and Suoh T (2002), Fashion: The Collection of the Kyoto Costume Institute: A history from the 18th to the 20th Century, Kyoto Fukushoku Bunka Kenkyu Zaidan. 8. Sengupta A K, Kothari V K and Alagirusamy R (1989), Characterization of the structural integrity of air-jet textured yarns, Textile Research Journal, 59(12), 758–762. 9. Sengupta A K, Kothari V K and Srinivasan J (1990), Effect of repeated laundering on the properties of air-jet textured cotton/filament composite fabrics, Textile Research Journal, 60(10), 573–579. 10. Sengupta A K, Kothari V K and Srinivasan J (1990), Air-jet texturing of twisted filament yarns using new jets: Part I: Influence of twist levels and direction of twist on the properties of air-jet textured yarns, Indian Journal of Fibre and Textile Research, 15, 154–158. 11. Sengupta A K, Kothari V K and Srinivasan J (1990), Air-jet texturing of twisted filament yarns using new jets: Part II: A comparison of yarn and fabric characteristics for equally bulked air textured yarns using zero-twist and pre-twisted feeder yarns, Indian Journal of Fibre and Textile Research, 15, 159–163. 12. Sengupta A K, Kothari V K and Srinivasan J (1990), Mechanism of the air-jet texturing process: Need for reappraisal, in Man-made fibre Year book, Chemiefasern Textilindustrie, 74–77. 13. Sengupta A K, Kothari V K and Srinivasan J (1991), Effect of process variables in air-jet texturing on the properties of spun yarns with different structures, Textile Research Journal, 61(12), 729–735. 14. Sengupta A K, Kothari V K and Srinivasan J (1991), Luft texturierung von Spinnfasergarnen – Vergleichder Gemeigenschaften Beiverschiedenen Strukturender Vorlagegarne [Air-jet texturing of spun yarns: A comparison of properties of textured yarns made using different parent yarn structures], Melliand Textilberichte (German edition), 72(6), 409–412. 15. Fellingham A (2002), Air-jet texturing, Sartex Textile Training, ISBN 1 85573 682 9, ISBN-13: 978 1 85573 682 5, CD-ROM, Woodhead, Cambridge, UK. 16. Manich A M, Maíllo J, Cayuela D, Gacén J, de Castellar M D and Ussman M (2007), Effect of the air-jet and the false-twist texturing processes on the stress-relaxation of polyamide 6.6 yarns, Journal of Applied Polymer Science, 105(5), 2482–2487. 17. Mukhopadhyay A, Dash A K and Kothari V K (2002), Thickness and compressional characteristics of air-jet textured yarn woven fabrics, International Journal of Clothing Science and Technology, 14(2), 88–99. 18. Swenson A (2008), Sensual Crochet, Luxurious Yarns, Alluring Designs, Sterling/ Hollan, New York. © Woodhead Publishing Limited, 2010
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19. Richard Horrocks A and Anand S (2000), Handbook of Technical Textiles, The Textile Institute, Manchester, UK; CRC Press, Boca Raton, FL; Woodhead, Cambridge, UK. 20. Australian International Design Awards, Optim™ Wool Fibre Processing Machine, available from http://www.designawards.com.au/application_detail. jsp?applicationID=2551 (accessed 14 September 2009). 21. Barella A (1983), Yarn hairiness, Textile Progress, 13(1), 1. 22. Bock G and Lunenschlob J (1982), Paper presented at the 66th Annual Conference of the Textile Institute, Textile Machinery: Investing for the Future, Lucerne, Switzerland. 23. Saville B P (1999), Physical Testing of Textiles, CRC Press, Boca Raton, FL, and Woodhead, Cambridge, UK. 24. Lawrence C A (2003), Fundamentals of Spun Yarn Technology, CRC Press, Boca Raton, FL, 1, 274. 25. Breward C (2003), Oxford History of Art: Fashion, Oxford University Press. 26. Schaffer C (2003), Sew Any Fabric: A Quick Reference Guide to Fabrics from A to Z, Krause Publications, Iola, WI. 27. Parks C (2007), The knitter’s Book of Yarn: The Ultimate Guide to Choosing, Using and Enjoying Yarn, Potter Craft, New York. 28. CSIRO, Cool light weight wools, Australia. Available from http://www.csiro.au/ files/files/p9u3.pdf (accessed 14 September 2009). 29. Kremenakova D (2005), Methods for investigation of yarn structure and properties, Czech Textile Seminar, Greece. Available from http://centrum.tul.cz/centrum/itsapt/ prezentace/wp2/Methods_structures.pdf (accessed 20 September 2009). 30. Yilmaz D, Göktepe F, Göktepe Ö and Kremenakova D (2007), Packing density of compact yarns, Textile Research Journal, 77(9), 661–667. 31. Renstrm B, Wool fibre properties a unique raw material, available from http://www3. cybex.gr/weissoutdoors/a.wool.htm (accessed 21 September 2009). 32. Oxtoby E (1987), Spun Yarn Technology, Butterworth, London. 33. Express Textile (2003), Saurer solutions for fancy yarns, available from http://www. expresstextile.com/20031002/productportfolio03.shtml (accessed 15 September 2009). 34. Brady G S, Clauser H R and Vaccari J A (2002), Materials Handbook: An Encyclopedia for Managers, Technical Professionals, Purchasing and Production Managers, Technicians, and Supervisors, Edition 15, McGraw-Hill, New York. 35. Özçelik G, Çay A and Kirtay E (2007), A study of the thermal properties of textured knitted fabrics, Fibres & Textiles in Eastern Europe, 15(1), 55–58. 36. Romer G and Bullinger R SAURER/ALLMA New Fashionator enlarges the possibilities for fancy ply yarns, available from http://www.ptj.com.pk/Web%202004/03-2004/ saurer1.html (accessed 20 October 2009). 37. Dugan J and Homonoff Ed, Synthetic split microfibre technology for filtration, available from http://www.fitfibres.com/files/microfibres%20for%20filtration.doc (accessed 18 October 2009). 38. Dugan J (1999), Critical factors in engineering segmented bicomponent fibres for specific end uses, available from http://www.fitfibres.com/files/Splittable%20Fibres. doc (accessed 18 October 2009). 39. Craik J (1993), The Face of Fashion: Cultural Studies in Fashion, Routledge, London. 40. Srinivasan J, Kothari V K and Sengupta A K (1988), Test methods for air-jet textured yarns, Indian Journal of Textile Research, 13, 97–106. © Woodhead Publishing Limited, 2010
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41. Srinivasan J, Kothari V K and Sengupta A K (1992), Air-jet texturing of spun cotton yarns for improved comfort; Part I: Influence of yarn structure on texturability, Textile Research Journal, 62(1), 40–43. 42. Srinivasan J, Kothari V K and Sengupta A K (1992), Air-jet texturing of spun cotton yarns for improved comfort; Part II: Texturability of carded spun yarns compared to combed spun yarns, Textile Research Journal, 62(3), 169–174. 43. Srinivasan J and Ramakrishnan G (2004), Study on high performance viscose micro fibres knitted fabrics, Asian Textile Journal, 13(10), 78–80. 44. Srinivasan J and Ramakrishnan G (2004), Study on viscose microfibres knitted fabrics, Proceedings of the International Conference on High Performance Textiles and Apparels (HPTEX 2004) held at Kumaraguru College of Technology (KCT), Coimbatore, India, organised by KCT, Coimbatore and TIEHH, Texas Tech University, Lubbock, TX, ISBN 81–7296-085-9, 292–299. 45. Srinivasan J, Ramakrishnan G and Mukhopadhyay S (2005), Study on high performance polyester micro denier fabrics, CD-ROM Proceedings of the International Conference on Advances in Textile Materials Technology, Management and Applications held at Kumaraguru College of Technology, Coimbatore, India, organised by KCT, Coimbatore and TIEHH, Texas Tech University, Lubbock, TX. 46. Srinivasan J, Ramakrishnan G, Mukhopadhyay S and Manoharan S (2007), A study on fabrics made from polyester micro denier fibre, Journal of the Textile Institute, 98(1), 31–35. 47. Kalyanaraman A R (1992), A process to control hairiness in yarn, Journal of the Textile Institute, 83(3), 407–413. 48. Cheng K B and Murray R (2000), Effects of spinning conditions on structure and properties of open-end cover-spun yarns, Textile Research Journal, 70(8), 690–695. 49. Kothari V K and Bari S K (2002), Properties of polyester/wool parent and air-jet textured yarns and their fabrics, Indian Journal of Fibre and Textile Research, 27(2), 156–160. 50. Chellamani K P and Chattopadhyay D (1999), Yarns and Technical Textiles, Monograph, Coimbatore, The South India Textile Research Association. 51. Schacher L, Adolphe D C and Drean J Y (2000), Comparison between thermal insulation and thermal properties of classical and microfibres polyester fabrics, International Journal of Clothing Science and Technology, 12, 2. 52. Microfibre, available from http://en.wikipedia.org/wiki/Microfibre (accessed 15 October 2009). 53. Microfibres, available from http://www.ivc-ev.de/live/index.php?page_id=75 (accessed 17 October 2009). 54. Microfibre cloths, available from http://totallymicrofibre.com/microfibre-cloths/ (accessed 18 October 2009). 55. Muratec Murata Machinery, Vortex spinning machine that creates new types of yarn, available from http://www.muratec-vortex.com/7_2.html (accessed 18 September 2009). 56. Walsh P (2006), The Yarn Book: Textile handbook: How to understand, design and use yarn, A&C Black, London. 57. Philips D G, Piper L R, Rottenbury R A, Bow M R, Hansford K A and Naylor G R S (1992), The significance of fibre diameter distribution to the wool industry, Review of a CSIRO workshop, CSIRO Division of Wool Technology, 27–28 November 1991, Report no. G72.
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58. Pillay K P R (1964), A study of the hairiness of cotton yarns, Part 1: Effect of fibre and yarn factors, Textile Research Journal, 34, 663–674. 59. Platt UK Ltd, The Platt Self Twist Spinner type 888, Lancashire. Available from http://www.macart.com/plattrepco.pdf (accessed 23 September 2009). 60. Popular clothing off-limits to Marines in Iraq, available from http://www.marines. mil/units/marforpac/imef/1stmlg/Pages/2006/Popular%20clothing%20off-limits%20 to%20Marines%20in%20Iraq.aspx (accessed 18 October 2009). 61. PrimaLoft® Insulation Technology, Introducing PrimaLoft® infinity, available from http://www.primaloft.com/outdoor/index.html (accessed 18 October 2009). 62. Lord P R, Mohamed M H and Ajgaonkar D B (1974), The performance of open-end, twistless, and ring yarns in weft knitted fabrics, Textile Research Journal, 44(6), 405–414. 63. Lord P R (2003), Handbook of Yarn Production: Technology, Science and Economics, Woodhead, Cambridge, UK. 64. Alagirusamy R and Ogale V (2004), Comingled and air jet-textured hybrid yarns for thermoplastic composites, Journal of Industrial Textiles, 33(4), 223–243. 65. Rengasamy R S, Kothari V K and Patnaik A (2004), Effect of process variables and feeder yarn properties on the properties of core-and-effect and normal air-jet textured yarns, Textile Research Journal, 74, 259–264. 66. Reports, summaries, studies and other publications of the United States International Trade Commission, International Trade Commission, Washington, DC, Office of the Secretary. 67. Gong R H and Wright R M (2002), Fancy yarns: their manufacture and application, The Textile Institute, Manchester, UK; Woodhead, Cambridge, UK; CRC Press, Boca Raton, FL. 68. Rozelle W N (1990), Slashing declares war on warp yarn hairiness, Textile World, 140(12), 71–76. 69. Rengasamy R S, Das B R and Patil Y B (2009), Thermo-physiological comfort characteristics of polyester air-jet-textured and cotton-yarn fabrics, Journal of the Textile Institute, 100(6), 507–511. 70. Saurer total solutions: Fancynation, available from http://www.oerlikontextile. com/Portaldata/1/Resources/saurer_textile_solutions/media_center/Fancynation.pdf (accessed 20 October 2009). 71. Ganesan S, Venkatachalam A and Subramaniam V (2007), Fibre migration in compact spun yarns: Part II – Mechanical compact yarn, Indian Journal of Fibre and Textile research, 32(2), 163–168. 72. Yoo S and Barker R L (2005), Comfort properties of heat-resistant protective workwear in varying conditions of physical activity and environment. Part I: Thermophysical and sensorial properties of fabrics, Textile Research Journal, 75(7), 523–530. 73. Smid J K (Bodegraven, Netherlands) and Terwee T H M (Wierden, Netherlands) (1983), Process for the manufacture of twistless or substantially twistless yarn and the yarn obtained according to this process, United States Patent 4395871, available from http://www.freepatentsonline.com/4395871.html (accessed 17 September 2009). 74. Mukhopadhyay S and Ramakrishnan G (2008), Microfibres, Textile Progress, 40(1), 1–86. 75. Gordon S and van der Sluijs R, Murata vortex spinning delivers cost savings to industry, available from http://www.csiro.au/science/MurataVortexSpinning.html (accessed 16 September 2009). 76. Anand S (2006), Medical Textiles and biomaterials for healthcare; Woodhead, Cambridge, UK. © Woodhead Publishing Limited, 2010
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77. Swicofil AG Textile Services, Emmenbruecke, Switzerland, Yarn and fibres in cashmere, available from http://www.swicofil.com/products/035cashmere.html (accessed 20 September 2009). 78. Textile Asia, 31, 7–12. 79. Textile Exchange, Bamboo fibre, a brief analysis, available from http://www.teonline. com/knowledge-centre/bamboo-fibre.html (accessed 12 September 2009). 80. Jonaitiené V and Stanys S (2004), Analysis of the properties of air-textured sewing threads, Fibres & Textiles in Eastern Europe, 12(1), 84–87. 81. Steele V (2005), Encyclopedia of Clothing and Fashion, Vol. 3, Scribner, New York. 82. Kothari V K, Sengupta A K, Srinivasan J and Goswami B C (1989), Air-jet texturing of cotton-filament composite yarns for better apparel comfort, Textile Research Journal, 59(5), 292–299. 83. Von Berger W (1954), Wool: history, grades and statistics, in Matthew’s Textile Fibres: Their Physical, Microscopical and Chemical properties, Chapter 6, HR Mauersberger (ed), 6th edition, Wiley, New York. 84. Wang X, Miao M and How Y (1997), Studies of JetRing spinning, part 1: reducing yarn hairiness with JetRing, Textile Research Journal, 67(4), 253–258. 85. Wang X and Miao M (1997), Reducing yarn hairiness with an air-jet attachment during winding, Textile Research Journal, 67(7), 481–485. 86. What are MicroFibres? Available from http://www.straw.com/cpy/wisdom/microfibres. html (accessed 18 October 2009). 87. Wang X (2000), Innovation in Spinning and Winding of Staple Yarns, 10th International Wool Textile Research Conference, Aachen, Germany. 88. Lipenkov Ya (1983), Wool Spinning, Vol. 1, Mir Publishers, Moscow. 89. Beceren Y and Uygun Nergis B (2008), Comparison of the effects of cotton yarns produced by new, modified and conventional spinning systems on yarn and knitted fabric performance, Textile Research Journal, 78(4), 297–303. 90. Khan Z and Wang X (2003), Post spinning yarn engineering, Textiles Magazine, 30(3).
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7
Assessing the weavability of technical yarns
B. K. B e h e r a, Indian Institute of Technology, Delhi, India
Abstract: The use of industrial fabrics is increasing due to their wide range of applications in agriculture, civil engineering, protection and safety, the automotive industry and transportation, Storage and packaging, medical and ecological sectors, sports and recreation. Special fibres and yarns with specific properties are being selected for producing these special fabrics. Woven fabrics are preferred as industrial textiles in situations where the requirements of fabric properties demand high strength and elongation uniformity, dimensional stability and a fairly good resistance to abrasion. The weaving process ensures high utilization of the strength characteristics of the initial fibrous material from which the fabric is manufactured. However, the weaving conditions for new yarns and complex fabric structures pose new challenges for weavers. Understanding yarn behaviour during weaving to achieve high loom shed efficiency and desired fabric quality has been a subject of great interest to weaving technologists. This chapter deals with the weavability of industrial yarns with reference to yarn quality and weaving performance. The term weavability refers to the relative weaving potential of yarns to sustain loom stresses to produce the best possible weaving performance. The weavability of a yarn is largely influenced by the quality of grey yarn and the treatment it receives in the process of sizing. Among various yarn quality parameters, yarn strength, yarn extension and their variation are the most important yarn properties influencing predominantly the warp breakage rate. Abrasion resistance and yarn hairiness are other important yarn properties which significantly affect the performance of yarn during weaving. The study of weavability also deals with fibre damage and structural distortion of yarns during weaving. The analysis of weavability therefore helps to preserve the strength characteristics of the parent yarn when weaving industrial textiles. Key words: inter-yarn friction, structural distortion, weaving stresses, warp breakage mechanism, yarn preparation, micro-denier yarn.
7.1
Weavability of yarns
In weaving, two sets of threads cross and interweave with one another. The yarns are held in place due to the inter-yarn friction. During weaving both warp and weft yarns are subjected to a certain amount of stress; a warp yarn has to undergo more complex stresses than a weft yarn. The resistance or capacity of a yarn to withstand these stresses is generally termed the weavability of that yarn. The study of weavability of warp yarn attracts the attention of weaving technologists as the majority of loom stops during weaving occur due 215 © Woodhead Publishing Limited, 2010
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to failure of warp yarns. The weavability of a yarn is largely influenced by the quality of grey yarn and the treatment it receives in the process of sizing. Among various yarn quality parameters, yarn strength, yarn extension and their variation are the most important yarn properties influencing predominantly the warp breakage rate. Abrasion resistance and yarn hairiness are other important yarn properties which significantly affect the performance of warp yarn during weaving. However, sizing takes care of these two properties and makes the yarn weavable. On the other hand, weft yarns are never sized. Only careful inspection and judicious clearing of these yarns during winding helps to enhance the weavability of the yarns. The strength of weft yarn has a direct bearing on the weft insertion rate of the loom. Broadly speaking, weavability refers to the weaving performance of yarns on the loom, which has a direct impact on loom stops and hence loom shed efficiency.
7.2
Importance of weavability in industrial fabrics
Woven fabrics are preferred as industrial textiles in situations where the requirements of fabric properties demand high strength and elongation uniformity, dimensional stability and a fairly good resistance to abrasion. The weaving process ensures high utilization of the strength characteristics of the initial fibrous material from which the fabric is manufactured. Therefore, it is important to preserve the strength characteristics of the parent yarn when weaving industrial textiles. The study of weavability also shows good correlation with fibre damage and structural distortion of yarns during weaving. Weaving technology has undergone dramatic changes during the last four decades. The conventional shuttle weaving system has been completely replaced by high-speed shuttle-less weaving techniques. The requirements of yarn quality and the preparation processes of the warp during winding, warping and sizing have also changed due to stringent demands for superior yarn quality to achieve the desired weaving performance. Most industrial textiles are made on standard weaving machines that are currently being used for the production of textile consumer goods. However, some more sophisticated industrial fabrics simply cannot be produced on the weaving machines currently available or have to be made of new unconventional textile materials which cannot be processed on such machines at all. To overcome such problems, new types of weaving machines have been developed and existing machines have been modified to produce speciality fabrics.
7.3
Factors influencing yarn weavability
There are numerous factors that affect the performance of yarn in weaving. They can be broadly classified under three heads: yarn quality, condition of warp preparation, and loom actions and conditions.
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7.3.1 Yarn quality Count strength product (CSP) Normally a weak, fuzzy and non-uniform yarn breaks often, whereas a strong, smooth and uniform yarn will be able to withstand the weaving stresses better. Among various yarn properties, the count strength product (CSP) is considered an excellent index for assessing the weavability of spun yarn. A high CSP yarn spun out of larger and finer fibre provides better inter-fibre locking and friction compared to a yarn spun out of short and coarser fibres. Sizing of warp yarn imparts the necessary protection to the yarn to withstand loom stresses, which the grey yarn does not possess. The extent of protection provided by the sizing to the yarn itself is a function of grey yarn quality. Sizing improves the weavability of a high CSP yarn better than that of a low CSP yarn. In the process of weaving, on account of weaving stresses, there is a continuous deterioration in almost all the properties of yarn. An assessment of the extent of degradation of yarn on account of weaving stresses can be made by determining the loss in weight of yarn in the case of grey yarn and the drop in strength in the case of sized yarn. A low CSP yarn deteriorates at a faster rate on account of weaving stresses than a high CSP yarn. This is of practical significance in understanding the weavability of yarns. It means that in actual weaving, a low CSP (weak) thread, by the time it reaches the healds and reed zone, becomes more susceptible to break than a high CSP (stronger) thread. It has been reported that the frequency of warp due to tensile-cum-abrasive failure exponentially decreases with increase in CSP. Single yarn strength It is well known that sizing improves yarn strength and that gain in strength increases with increase in size add-on. At very high add-on values the yarn becomes stiffer and less flexible because of a thick shell of size encapsulating the yarn and a deeper penetration. Single yarn elongation The process of sizing reduces the breaking elongation of grey yarn. This loss in yarn elongation during sizing takes place because of the following factors: ∑ ∑ ∑
The cementing of the fibres by size paste which precludes the inter-fibre slippage The tension applied on the warp sheet in sizing The yarn drying conditions.
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Although the yarn strength increases on sizing, probably due to an increase in yarn cohesiveness and prevention of inter-fibre slippage, yarn tenacity probably is not a critical property, since the tensile force exerted on yarn during weaving is much lower than its original strength. Yarn extensibility on the other hand is more important if the yarn is to withstand the cyclic extension and abrasion. Yarn abrasion resistance The size parameters such as size add-on and type of sizing ingredient used govern the abrasion resistance of yarn. The same yarn sized with sizing agent having low adhesion power gave a higher warp breakage rate than yarn sized with agent having moderate adhesion power. The abrasion resistance increases with the increase in size add-on. The wide range of abrasion resistance of a yarn along its length is caused by differences in the twist of the thickest places, which are due to the modulating influence of the spinning system. There is a certain minimum value of abrasion resistance below which the warp breakage rate increases sharply. Yarn hairiness The application of the size-coat on the yarn itself reduces the hairiness to an extent. A negative exponential relation has been established between sized yarn hairiness and size add-on. Classimat faults The classimat faults such as C3, C4, D3 and D4 classes are particularly weak in terms of tensile strength, elongation and abrasion to sustain the loom stresses, so it would be preferable to remove these faults in winding. Faults such as those in the A4 and B4 categories may be cleared in winding on the basis of their bulk and likelihood of getting trapped in the reed in weaving. From the studies carried out by various researchers on the effect of classimat faults on weavability, it has been established that the presence of A3 and A4 faults does not affect the strength and elongation of normal grey yarn. The realization of strength and elongation is minimum in the case of D3 and D4 faults. On sizing, except in the case of D 3 and D4 faults, the realization factor of strength and elongation of faults decreases. The D3 and D4 faults register the maximum gain in strength on sizing. Faults introduce into the yarn a very high frequency of low strength, elongation and abrasion resistance of threads, even lower than the minimum of normal yarn. When subjected to tensile load, many of the faults showed a prominent stick–slip phenomenon in the load–elongation curve. The frequency of
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yarn breaks at or in the vicinity of faults increases with fault size-length and cross-section.
7.3.2 Yarn preparation Appropriate yarn preparation for warp and weft is essential for achieving the highest possible and most economic weavability. Yarn preparation includes winding, doubling, warping, sizing, healding and reeding of warp yarn. There is no difference between the winding process and machines used to prepare the yarn for weaving consumer or industrial textile fabrics. Normally conicalshaped packages are preferred for spun yarn and ‘pineapple’ packages are used for filament yarn. Cylindrical packages are often used for polyolefin tapes for production of some industrial fabrics. The doubling of yarns is an important operation in the production of industrial textiles because it is seldom possible to achieve the desired strength with single yarns which can meet the weavability requirement in weaving without sizing. Moreover, the strength of the constituent fibres is better utilized in a doubled yarn. The most progressive machine for this purpose is the two-for-one twister. Since most industrial fabrics use coarser yarns, the machine is provided with a draw-off system situated between the spindle and the winding take-up mechanism to overcome the high tension in the yarn processed. The prerequisites of a well-prepared warp for achieving higher weavability include uniform tension in all ends of the warp sheet, proper and uniform hardness of the warp beam, a precise cylindrical shape of the warp beam and absence of any crossed and broken ends. In some cases, when industrial fabrics such as tyre or belting duck are produced, the warps are fed to the weaving machine directly from a number of warp rollers carrying warps with partial sett. In another system of producing low-sett industrial fabrics, the warp ends are unwound from individual cylindrical packages put up in a special creel situated behind the weaving machine. This system of weaving needs a very large area of floor space. To meet the requirement of the largescale production of industrial fabrics with comparatively low warp sett such as polypropylene tape backings for tufted carpets, coverstock and packaging materials, special warping machines have been developed in which the warp is prepared in full warp sett and width in a single operation. Sizing makes the yarn weavable by imparting the essential properties such as abrasion resistance and subdued hairiness, which the yarn does not possess. The objective of sizing is to improve a number of grey yarn properties such as strength, toughness, modulus, hairiness, abrasion resistance, etc. However, the prime objective of sizing is to impart a reasonably thick band of size film around each individual yarn and to ensure a certain amount of size penetration to provide film–fibre anchorage and hence to give a binding
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effect. All these effects combined together enable the yarn to sustain weaving stresses or in other words, improve weavability.
7.3.3 Loom actions and conditions During weaving warp yarn is subjected to cyclic elongation, axial abrasion and flexing action. The reed exerts a rubbing action in its movement along the yarn, while the latter moves at right angles to the reed. The pick being moved into the clothfell rubs the warp yarn more particularly when the shed is closing. It was found that early shedding gave low warp tension but the amount of abrasion was at maximum. The bottom part of the shed frequently rubs the race-board and the shuttle abrades the warp yarn in the longitudinal and transverse direction. Wear of the yarn by abrasion increases with the warp and weft density. The motion of the shaft and the beat-up of the reed cause the tension fluctuations. The resistance of the yarn to repeated stresses of this type is called fatigue-strength. Tensile deformation accelerates yarn failure due to abrasion while the abrading action accelerates yarn failure as a result of tensile deformation. The fibres are loosened out of the yarn structure by the abrading action of the loom parts and form rings around one or more yarns. Other conditions being equal, the intensity of destructive action, in the form of friction on the back rest, in the heald eye, dropper and reed dents, depends on the magnitude of the reciprocating movement of the warp yarn and repeats of this movement. Besides these, the type and count of healds, staggering of healds, type of reed, air space, baulk length, reed, etc. also affect the weavability of warp yarn. On account of loom stresses a warp yarn can break in the following five manners: 1. The abrasive action is normal but the abrasion resistance of the yarn or a part of it is insufficient to withstand it. 2. The repeated stretching as applied to the yarn is normal but the resistance of the yarn to this repeated stretching – the dynamic strength and the residual sized yarn elongation – is too low. There are also weak spots in the yarn. 3. The abrasion resistance of the yarn is normally sufficient but the abrasive action of a part of the loom and the warp density are both too high. 4. The dynamic strength of the yarn is normally sufficient but the strain of the repeated stretching is too high. 5. Finally, warp breaks may be caused by incidental or occasional occurrences such as an incidental high tension peak. Causes 1 and 2 originate in defects in the process of spinning or yarn preparation sizing. Poor grey yarn quality in terms of strength, twist (multiplier) and the presence of a higher frequency of imperfection also lowers the abrasion
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resistance of the yarn considerably, either in the damaged part of the loom or in the presence of imperfections in the yarn.
7.4
Warp breakage mechanism
In the process of weaving, the warp yarn is subjected to complex mechanical actions. Some of these actions and their locations are listed in Table 7.1. As mentioned earlier, warp yarn undergoes three major stresses such as cyclic extension, flexing and axial abrasion, and normally a warp yarn does not break because of lack of strength during the weaving operation. The strength of yarn in fact is much greater than the average tension imposed on it due to weaving stresses. Rather, abrasion between neighbouring yarns and with the machine elements is significantly responsible in this regard. As weaving progresses, this repeated abrasion action loosens the yarn structure and as a result some protruding fibres come out from the yarn body and fuzzball formation takes place on the yarn surface. Removal of one or a few fibres from the yarn structure creates a void in the yarn body which facilitates easy movement of the constituent fibres, called inter-fibre slippage. This process continues and finally causes complete distortion of the yarn structure and a breakage occurs. Figure 7.1 demonstrates how a single unsized yarn fails because of surface damage and fibre entanglement causing fuzzball formation on the yarn surface. The fibres accumulating on the surface no longer contribute towards the axial strength, as a result of which slippage occurs between the remaining fibres in the cross-section and the yarn fails. It is therefore important to apply a sort of protective coating of an adhesive, which lays the protruding fibres on the body of the yarn, thus reducing the friction to the yarn as it passes through the loom parts. This presents tremendous scope to improve weavability and fabric quality through sizing of single yarns. In contrast to unsized yarns, sized yarn does not fibrillate so easily because of fibre consolidation by the adhesion of the size material with the fibre substrate. Rather the failure occurs due to fibre breakage as shown in Fig. 7.2. Moreover, the fibres in the cross-section of the yarn act in aggregate and Table 7.1 Stresses on yarn due to loom actions Loom action
Location
1. Flex abrasion
Back roll, healds, dropwires and fell of cloth Any part where yarn contacts moving parts Healds and reed motion
2. Scraping abrasion 3. Yarn-to-yarn abrasion, cyclic stretching, bending and entanglement 4. Shuttle–yarn collision
Shed opening
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7.1 Failure mechanism of single unsized yarn.
7.2 Failure mechanism of single cold sized yarn.
not individually, thus enhancing the mechanical properties and weavability of the yarn. Most industrial fabrics are produced with heavy construction and therefore use doubled yarn. Yarn mechanical properties are considerably improved by plying but ultimately two-ply yarn breaks when one of the component yarns fails. Failure occurs basically by fibre slippage as normally these yarns are not sized. The structural disintegration in this case is somewhere between that of single unsized and sized yarn as shown in Fig. 7.3.
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7.3 Failure mechanism of two-ply unsized yarn.
7.5
Analysis of warp breakage mechanism
Failure mechanism of spun yarns under fatigue and abrasion actions has been extensively studied by many researchers. The warp breakage mechanism has been investigated by various methods in order to analyse causes of warp yarn failure on the loom during weaving. Some of the important methods include statistical analysis of yarn failure data, analysis of fatigue behaviour of yarn under weaving stresses, quantitative analysis of structural stability, examination of yarn/fibre damage by scanning electron microscopy, and quantitative analysis of structural distortion by digital image processing. It is established that the nature of yarn failure mainly depends on yarn structure and spinning technology. For example, inter-fibre slippage is predominant in warp breakage of friction spun yarns as compared to ring apun yarns where fibre breakage also plays an equally important role. Dref yarn exhibits low fatigue resistance and poor structural stability as compared to ring and rotor yarns. Among all technical yarns, normally failure occurs at minimum yarn diameter and at maximum change in the yarn diameter.
7.6
Evaluation of weavability
It is important for the weaver to estimate the warp breakage rate for a given yarn quality before the yarn is actually woven in the loomshed. The approaches used so far to estimate the warp breakage rate can be broadly classified into the following classes: ∑ Empirical
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∑ ∑
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Statistical Instrumental.
7.6.1 Empirical approach In weaving, the yarn is subjected to various types of stresses such as tensile, cyclic extension, compression and bending. When a yarn is subjected to such repeated stresses, the stress builds up within it, increasing continuously, and when this stress becomes sufficiently large to overcome the cohesive forces within the yarn, break occurs. The failure of a yarn under the cumulative application of repeated or cyclic stress is known as fatigue failure. During this cycle, rupture usually initiates at some structural imperfection in or on the yarn, which grows with the number of cycles and finally weakens the yarn so that it breaks. Because of the frequency of imperfections and the non-uniformity of the yarn structure, the individual values of fatigue life are normally expected to be scattered over a fairly wide range, within which the extreme values (i.e., lowest strength or shortest life) are of most significance in predicting the weavability of yarns. The frequency of such threads may therefore be a good index of the weavability of yarns. For this purpose, it is necessary to understand the statistical nature of the distribution of fatigue life cycles.
7.6.2 Statistical approach As early as 1923 owen and oxley recognized the statistical nature of the process of yarn failure. They determined a frequency distribution for the fatigue lifetime of a cotton yarn by testing successive lengths from single bobbins. They discovered certain lifetime periodicities along the length of the yarn and advanced the view that relatively long specimens are more likely to contain weak points than shorter specimens, and thus might be expected to have shorter lifetimes. In another line of approach to understand the probability distribution of the lowest elemental strength of a composite (yarn), Pierce followed exactly the same procedures, which are used by statisticians in the area of extreme value statistics. Gumbel has described the derivation of the probability distribution of extreme values drawn from three types of parent population in the limits of indefinitely large sample (composite) sizes. These expressions have become known as asymptotic probability distributions of the largest and smallest extreme values or simply as asymptotes. A third asymptote, in particular, has been extensively used by Weibull and others in the statistical analysis of fatigue lifetime data for metals; hence it is widely known as the Weibull distribution. Weibull stressed the fact that the normal and the logarithmic normal distributions seldom provide a good fit of lifetime data. The suitability of the weibull distribution
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was confirmed for viscose, nylon and polyester mono-filament yarns, sized and unsized cotton yarns, sized worsted yarns and woollen yarns. Weibull himself has stressed that although a good fit may be apparent in the median region of the distribution, there are usually large discrepancies at the tails. In addition, lifetime distributions are generally unsymmetrical. Because of these limitations, the Weibull distribution could not be used with confidence for predicting the warp breakage rate.
7.6.3 Instrumental approach In order to find a more expedient method, attempts have also been made to simulate the weaving conditions in the laboratory. For this purpose two approaches have been used: firstly, to measure the shed droppings during testing, and secondly, to measure the number of abrasion or stress cycles required to break the desired number of specimens. Using the first line of approach two shed testers were developed. These were simpler to operate than the loom and had fewer adjustments. The shed (droppings) were defined as the mass of fibres and size abraded from the yarn during weaving; this was the dependent variable in the experiments and was taken as a convenient measure of weavability. Shed is produced in the weaving process by the abrasion of yarn against yarn and of yarn against metal. This also causes the yarn to rupture as sufficient numbers of fibres are rubbed off the yarn. Often these short fibres collect on the yarn in the form of small, tangled aggregates that became lodged in the metal parts of the loom and cause the breakage. Finally they may wrap around adjacent yarns and reduce the opening of the shed. This puts excess tension on the yarns and may cause them to break. Using this idea a number of instruments were developed in which the sized yarn sheet was subjected to cyclic flexure combined with abrasion against yarns and metal surfaces such as healds and reed. These devices proved to be a definite improvement over others but suffered from the difficulty involved in reproducing the results. Attempts were also made to develop some special devices combining both of the two approaches used earlier. Although there had been an immense amount of work on the development of instruments, the major difficulty experienced with these numerous abrading devices had been that of correlating the results with those found from full-scale weaving trials. More recently, work to develop an instrument for the assessment of the weavability of sized yarns has been carried out by Trauter (the Reutlinger Web Tester) and by Miller et al. at the Textile Research Institute (the Cyclic Tensile Abrader). The Reutlinger Web Tester can simulate all the more important loads and stresses occurring in weaving, such as cyclic elongation, axial abrasion and buckling, as in weaving these loads are applied simultaneously on the yarn. A satisfactory correlation between values from the Reutlinger Web Tester and
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yarn behaviour in weaving has been found. Over 80% of the tests conducted in parallel with the weaving industry show that a higher web tester value corresponds to a better weavability of warp. Although, this instrument has given a new means of assessing the weavability of warp yarns, it cannot fully replace actual weaving trials to assess weavability, but it does allow for a considerable reduction in the number of trials on weaving machines. Miller and colleagues of the Textile Research Institute, Princeton, NJ, have developed another apparatus, the cyclic Tensile Abrader, that imposes an adjustable constant axial tensile load on filaments, yarns or fabric strips during cyclic rubbing over pins in various configurations and under controlled temperature and specific chemical environments. The action is intended to simulate the combination of tensile, bending and abrasive stresses experienced by fibrous materials during processing and end-use. These instruments, no doubt, are a definite improvement over the laboratory tests, but neither of them can be used with confidence to predict the actual warp breakage rate in weaving. The major limitation of these techniques is that they simply evaluate or relate without considering the faults present in the sized yarn. Therefore, the results obtained from these instruments can be considered as providing the relative weaving potential of the yarns.
7.7
Weavability of synthetic filament yarn
The increasing share of artificial fibres in the woven fabric sector, together with the relative difficulty in handling these fibres during winding, warping and sizing, has attracted a considerable attention to this subject in recent years. High tensile strength and elongation at break, excellent resilience, smooth surface, hydrophobicity and thermoplasticity are some of the outstanding properties of most commercial synthetic fibres which enabled them to be used for many industrial applications. However, preparation of these yarns for weaving is somewhat difficult as the basic principles underlying the processing of these yarns are preservation of extensibility, avoiding partial fusion of the yarn and protection from filamentation of components. Continuous filament warp yarns can be made weavable by either twisting, intermingling or sizing. In all three alternatives, cohesion between the neighbouring filaments of the multi-filament yarn is generated, which holds the fibres together and reduces separation and filamentation during weaving. The three different types of filament warp preparation along with their relative advantages and disadvantages are shown in fig. 7.4. In both twisting and intermingling, the yarn physical structure alters, whereas sizing is the only process which enhances the weavability of a warp without disturbing the surface characteristics of the yarn. So, the choice of a particular process is largely dependent on the end use of the fabric to be produced.
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(1) Produces crispy handle fabric, such as voil, chiffon, georgette, etc. (2) Process is cheaper
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Twisting
Disadvantages: (1) Feeling is harsher (2) Change in physical structure
2. Intermingling Advantages: (1) Process is cheapest Disadvantages: (1) Yarn gives subdued lustre and fabric gives reduced shining effect (2) Change in physical structure
3. Sizing Advantages:
(1) Fuller and softer handle is possible (2) Increased shining in fabric (3) No change in physical structure
Disadvantages: (1) Process is costlier
Intermingling
Sizing Desizing
7.4 Different means of preparation of filament warp.
7.7.1 Evaluation of weavability of sized filament yarn In order to evaluate the weavability of sized filament yarn it is essential to understand how the warp yarn breaks on the loom due to weaving stresses. The breakage mechanism of filament yarn during weaving abrasion is shown in fig. 7.5. The figure illustrates gradual filamentation and fuzzball formation on the yarn surface. In fact, breakage of sized multifilament warp during weaving starts with separation of individual monofilaments. Individual filament break is initiated in a multifilament yarn when it is subjected to loom stresses. Due to the oscillating action of various parts, the broken filament begins to peel back and subsequently it entangles with the neighbouring filaments and causes the rupture of the other filaments. Finally this results in complete yarn failure for one of two reasons. Either a weak spot is formed which breaks easily since the load is distributed over fewer filaments, or the fuzzball becomes large enough to catch on a loom part which ultimately results in yarn breakage.
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(A)
(G) A multifilament
Prevention fo peeling back
(B) Breaking of individual filament
(C) Peeling back of broken filament
Fuzzball formation
Due to entanglement with neighbouring filaments (D) Rupture of other filaments
Due to either: 1. formation of weak spot, or 2. formation of larger fuzzball to catch on loom part
(E) Complete failure
Spot-welded filaments
(F) Sized yarn Split filament
7.5 Breakage mechanism of filament yarn during weaving.
Sizing binds multifilament yarn together to prevent separation and entanglement and also to form a flexible outer film which will protect the yarn against abrasion and prevent broken monofilaments from peeling back along its length. Therefore, the degree of separation of sized and bound filament into groups and the extent of peeling of the broken filament should give an indirect measure of weaving potential of a sized multifilament yarn.
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Degree of detachment-1 (DD-1) DD-1 can be estimated by measuring the extent of yarn splitting under a microscope, when the yarn is subjected to tensile extension. In this method, basically a number of individual and group filaments are counted after loading the yarn to a predetermined level of extension, and DD-1 is calculated in terms of the percentage of separated filament groups to the total number of filaments present in the yarn. Degree of detachment-2 (DD-2) DD-2 can be estimated by measuring the extent of yarn separation as in the case of DD-1, but subjecting the warp yarn to certain important weaving stresses such as cyclic elongation, abrasion and buckling on a weavability tester simulated with these stresses. According to these two measurements, a degree of detachment of 100% prevails if none of the individual filaments stick together, and a degree of detachment of zero results when no filament is separated, i.e. the yarn behaves as a single rod as in the case of a completely bound sized yarn. Filament peeling resistance (FPR) The FPR of sized filament yarn can be determined according to the standard described by Bradbury in which sized yarns are subjected to weaving stresses on a weavability tester for a particular duration with a predetermined tension. Under these conditions the broken filaments resulting from complex weaving stresses on the yarn peel back and the distance to which they peel back is measured under a microscope to give a quantitative value of peeling resistance.
7.8
Sizing of micro-denier yarns for achieving desired weavability
Micro-fibres are used for many speciality fabrics, particularly where soft feel and close spacing of threads are required. These yarns possess promising features for consumers, set new standards for aesthetics, and have incredible performance qualities. However, they are fragile and need special care during preparation as well as weaving. To slash micro-denier yarns for maximum weaving efficiency one must ensure correct stretch tension. Packages should be handled with maximum caring in the warping creel. The tension devices should be of an electrical type to ensure exact tension settings. Drop-wires, collecting eye-board and combs must have no worn areas. They must be cleaned on a predetermined schedule to prevent different fibre finishes from
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causing an accumulation problem. Proper beam tension is critical and must be determined for each beam, yarn type, style, etc. Provision of static bars is needed along the yarn path to prevent static generated from increased surface areas, more filaments and the tendency to wear any surface the yarn contacts. Both conventional cotton-system slasher and single-end sizing machines are used to size micro-denier filament yarns. Most conventional filament slashers can process twisted micro-denier yarns, but a pre-drying unit is mandatory for low- and zero-twist yarns. Also a hook reed needs to be located prior to the size box entry to keep yarns straight and orderly.
7.9
Bibliography
1. Behera B.K. and Hari P.K., Weaving performance of polyester blended sized yarns: roles of size recipe and high squeeze pressure, Indian journal of fibre and textile research, Vol. 18, June 1993. 2. Behera B.K. and Hari P.K., Mechanism of yarn break for high-pressure squeezed sized yarn, Indian Journal of Fibre and Textile research, Vol. 18, December 1993. 3. Behera B.K., Micro fibres – outlets and challenges, Textile Asia, March 1995. 4. Punj S.K. and Behera B.K., Polyester – viscose variations, Textile Asia, March 1995. 5. Behera B.K. and Pakhira A., Studies of structural changes and damage of polyester filament yarn during sizing, Journal of the Textile Institute, Vol. 89, No. 3, 1998. 6. Behera B.K. and Pakhira A., Evaluation of weavability of polyester multi-filament sized yarn, Journal of the Textile Institute, Vol. 89, No. 3, 1998. 7. Behera B.K. and Basu S., Studies on weavability of polypropylene spun yarn, Indian Journal of fibre and Textile Research, Vol. 26, June 2001. 8. Behera B.K., Hari P.K. and Ghosh S., Weavability of compact yarn, Melliand International, Vol. 9, No. 4, 2003. 9. Behera B.K. and Joshi V.K., Weavability of Dref-2 yarn, Indian Journal of Fibre and Textile Research, Vol. 29, No. 3, 2004. 10. Behera B.K. and Joshi V.K., Weavability of ring, rotor and friction spun yarn – Performance of unsized yarn, Textile Asia, Vol. 36, No. 10, 2005, p. 34. 11. Behera B.K. and Joshi V.K., Weavability of ring, rotor and friction spun yarn – Performance of sized yarn, Textile Asia, Vol. 36, No. 11, 2005, p. 34. 12. Behera B.K. and Joshi V.K., Effect of sizing on weavability of dref yarn, Autex Research Journal, Vol. 6, No. 3, 2006, pp. 142-147. 13. Behera B.K. and Joshi V.K., Warp breakage mechanism for friction spun yarns, Journal of the Textile Institute, Vol. 97, No. 6, 2006. 14. Behera B.K. and Mishra R., Weavability of non-conventional worsted warp yarns, Journal of Textile Engineering, The Textile Machinery Society of Japan, Vol. 52, No. 3, 2006. 15. Behera B.K. and Joshi V.K., Weavability of core spun dref yarn, Indian Journal of Fibre and Textile Research, Vol. 32, No. 1, 2007, pp. 40–46. 16. Behera B.K., Gupta R. and Mishra R., Statistical modelling of weavability of different size materials, Melliand Textile International, No. 4, 2007. 17. Behera B.K., Studies on high pressure sizing, Ph.D. thesis, IIT Delhi, 1989. 18. Aggarwal S.K., Ph.D. thesis, IIT Delhi, 1987.
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19. Pakhira A., M.Tech thesis, IIT Delhi, 1994. 20. Gandhi R.S. and Talele A.B., Sizing of filament yarn, National Symposium on Sizing, Ahmedabad, India, 1991. 21. Aggarwal S.K. and Subramaanian T.A., Prediction of warp breakage rate in weaving, Textile Research Journal, Vol. 58, No. 1, 1988, pp. 11–21. 22. Hari P.K., Aggarwal S.K. and Subramaanian T.A., Contribution of yarn quality and sizing to the weavability of yarns, paper presented at the 7th International Sizing Symposium, Mulhouse, France, October 1986. 23. Aggarwal S.K. and Hari P.K., Use of tensile strength on characterizing repetitive stress in weaving, Indian Journal of Textile Research, Vol. 13, December 1988, p. 198. 24. Aggarwal S.K., Hari P.K. and Subramaanian T.A., Evaluation of classimat faults for their performance in weaving, Textile Research Journal, Vol. 57, December 1987, p. 735. 25. Hari P.K., Aggarwal S.K. and Subramaanian T.A., Phenomenon of warp breakage in weaving, Indian Journal of Textile Research, Vol. 14, March 1989, p. 31. 26. Anandjiwala R.D. and Goswami B.C., Analysis of fatigue phenomenon of warp yarn, AATCC Symposium, 1993. 27. Anandjiwala R.D. and Goswami B.C., Tensile fatigue behaviour of staple yarns, Textile Research Journal, Vol. 63, No. 7, 1993, p. 392. 28. Anandjiwala R.D. and Goswami B.C., Reply to comments on tensile fatigue behaviour of staple yarns, Textile Research Journal, Vol. 64, No. 8, 1994, p. 491. 29. Anandjiwala R.D., Carmical M. and Goswami B.C., Textile properties and static fatigue behaviour of cotton warp yarns, Textile Research Journal, Vol. 65, No. 3, 1995, p. 131. 30. Frank F. and Singleton R.W., A study of factors influencing the tensile fatigue behaviour of yarns, Textile Research Journal, Vol. 34, No. 1, 1964, p. 11. 31. Picciotto R. and Hersh S.P., Tensile fatigue behaviour of a warp yarn and its influence on weaving performance, Textile Research Journal, Vol. 42, 1972, p. 512. 32. Slauson S.D., Miller B. and Rebenfeld L., Physicochemical properties of sized yarns. Part I: Initial studies, Textile Research Journal, Vol. 54, 1984, p. 655. 33. Realff M.L., Seo M., Boyce M.C., Schwartz P. and Backer S., Mechanical properties of fabrics woven from yarns produced by different spinning technologies: Yarn failure as a function of gauge length, Textile Research Journal, Vol. 61, No. 9, 1991, p. 517. 34. Nanjundayya C., Strength of a cotton yarn with particular reference to the structure at the region of break, Textile Research Journal, Vol. 36, No. 11, 1966, p. 954. 35. Seo M.H., Realff M.L., Pan N., Boyce M., Schwartz P. and Backer S., Mechanical properties of fabric woven from yarns produced by different spinning technologies: Yarn failure in woven fabric, Textile Research Journal, Vol. 63, No. 3, 1993, p. 123. 36. Cybulska M., Analysis of warp destruction in the process of weaving using a system for the assessment of yarn structure, Fibres & Textile in Eastern Europe, Vol. 5, No. 4, 1997, pp. 68–72. 37. Cybulska M. and Goswami B.C., Failure mechanism in staple yarns, Textile Research Journal, Vol. 71, No. 12, 2001, p. 1087.
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8
Yarn imaging and advances in measuring yarn characteristics
R. F a n g u e i r o and F. S o u t i n h o, University of Minho, Portugal
Abstract: This chapter discusses two integrated fields, the imaging techniques applied to yarn structures, and the latest advances in measuring yarn characteristics. The chapter first reviews the use of digital image processing in yarns, considering its importance, applications and recent advances. The chapter then discusses new developments in measuring yarn characteristics and online systems for measuring yarn quality. Key words: yarn imaging, digital image processing, special measurements, online systems.
8.1
Introduction
Image processing and analysis can be defined as the act of examining images for the purpose of identifying objects and judging their significance. [1] Image analysis studies remotely sensed data, using logical processes to detect, identify, classify, measure and evaluate the significance of physical objects, their patterns and spatial relationships.
8.1.1 The concept of image An image contains descriptive information about the object it represents. Images occur in various forms, some visible and others not, some abstract and others physical, some suitable for computer analysis and others not. It is thus important to be aware of the different types of images. [2] Images can be classified into several types, based on their form or their method of generation. [2] It is instructive to employ a set theory approach. If a set of objects is considered, and images form a subset thereof, there is a correspondence between each image in the subset and the object represented. Within the set of images itself, there is a very important subset containing all the visible images – those which can be seen and perceived by the eye. Within this set again, there are several subsets representing the various methods of generating the image. These include photographs, drawings and paintings. Another subset contains optical images, that is, those formed with lenses, gratings and holograms. Figure 8.1 represents this schematically. 232 © Woodhead Publishing Limited, 2010
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Images Visible images Mathematical functions Continuous Objects
Discrete (digital images)
Pictures Photographs Drawings Paintings
Non-visible physical images
Optical images
8.1 Image classification.
8.1.2 Importance of image processing in industrial processes Image processing techniques are based on using analogue or digital optoelectronic devices and systems that allow an image with specific information distribution to be placed at the input or output of the system. [3] In the past, many tasks in manufacturing, such as inspection and assembly, were performed by human operators. Systematic assembly and inspection operations performed in an appropriate sequence or implemented in parallel lend themselves to image-controlled automation. The necessary functions for imaging equipment include: [4] ∑ Exploiting and imposing environmental constraints ∑ Capturing an image ∑ Analysing the image ∑ Recognizing certain objects within it ∑ Initiating subsequent actions in order to complete the task at hand. Remotely sensed data are analysed using various image processing techniques and methods, including analogue image processing and digital image processing. [1] Visual/analogue processing techniques are applied to hard-copy data such as photographs or printouts, and interpret particular elements of the image. Whether analogue or digital, the image processing technique includes image
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recognition and computer graphics. Image analysis is connected with image detection and processing, projection, transmission and storage, as well as image recognition and generation. Important applications of image processing include industrial machine vision applications (automated visual inspection, process control, parts identification, robotic guidance and control), space exploration, astronomy, diagnostic medical imaging (medical image processing, medical image reconstruction) and scientific analysis. [4] Nowadays, image processing techniques are developing rapidly due to advances in informatics (information science and technology) and microprocessing technology.
8.1.3 Digital image processing Digital image processing comprises a collection of techniques for manipulating digital images using computers [2] and has been applied to almost every type of imagery, with different degrees of success. Digital image techniques have been used in textiles for years [5], mainly for examining and analysing the structural parameters of yarns. At its most basic level, digital image processing requires a computer to process images and two pieces of special equipment, an image digitizer and an image display device. In their standard form, images are not directly amenable to computer analysis. Since computers work with numerical (rather than pictorial) data, an image must be converted to numerical form before it can be processed by a computer. Figure 8.2 shows a proposed system for image processing. The digital image produced by the digitizer goes into temporary storage on a suitable device. In response to instructions from
Monitoring
Image acquirement system
Sampling and quantification
Record on disc memory
Memory actualization Processing
Fibrous structure
Digitization
Computer
Memory buffer
Receiver
Display Output
8.2 System for image processing [3].
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the operator, the computer executes image-processing programs on images called up from a library. During execution, the input image is read into the computer line by line. Digital analysis can be used for identifying and measuring the geometrical dimensions of textile objects with very small dimensions; in particular, it enables the structure of the objects investigated to be analysed. [6]
8.2
Image processing techniques in fibrous material structures
8.2.1 Introduction to image processing techniques in fibrous materials structures Computer vision is becoming more affordable both as a research tool and in process quality control. It has the advantage of providing more extensive characterization of the test product, at high speeds and resolutions, as well as being non-contact. [7] Electronic images contain more visual information than the human eye can discern. After a textile product is imaged, procedures may be used to yield more detailed structural conformation and to calculate different parameters. [8] Image processing techniques have been applied to pilling evaluation, fabric texture and defect recognition, drape analysis, morphological measurements of fibre, and grading yarn appearance. [9] Digital image analysis also permits a more detailed study of the basic structural parameters of linear textile products, such as thickness, hairiness and number of twists. [6] In addition, this technique enables the above characteristics and others, such as twist parameter and linear density coefficient, to be estimated. Image processing techniques can be used to image longitudinal and transverse cross-sections of fibres, fibre diameters, and linear textile products, which allows possible yarn faults and their causes to be determined. The images obtained can help to create two-dimensional (2D) and three-dimensional (3D) textile products. Digital image processing of textile product images is mainly concerned with processing 2D images. Imaging techniques can be used to obtain detailed information about fibrous structures in the laboratory as well as in the production environment. Such evaluation has positive implications for measuring textile quality during production. [8]
8.2.2 Basic concepts used for digital image processing in fibrous material structures Digital analysis of 2D images is based on processing the image acquired using a computer. The image is described by a 2D matrix of real or imaginary
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numbers represented by a definite number of bytes. [3] Digital image processing includes: [3] ∑ Image acquisition and modelling ∑ Improving image quality and highlighting distinguishing features ∑ Reinstating the desired image features ∑ Compressing image data. Image modelling is based on digitizing the real image. This process consists of sampling and quantifying the image. The digital image is defined by spatial image and grey-level resolution. The smallest element of the digital image is called a pixel. The number of pixels and the number of levels of brightness may be unlimited. [3] Improving image quality and highlighting distinguishing features are the most commonly used techniques in image processing. The process of improving image quality does not increase the essential information represented by the image data, but increases the dynamic range of selected features of the acquired object, which facilitates their detection. [3] Reinstating desired image features is connected with eliminating and minimizing any image features which lower its quality. Acquiring images by optical, optoelectronic or electronic methods involves the unavoidable degradation of some image features during the detection process. Aberrations, internal noise in the image sensor, blurring caused by camera defocusing, as well as turbulence and air pollution in the surrounding atmosphere, may affect quality. [3] Image data compression is based on minimizing the number of bytes needed to represent the image. The compression effect is achieved by transforming the given digital image to a different number table in such a manner that the preliminary information is packed into a smaller number of samples. [3] The main problem with analysing the structural parameters of textiles is the quality of the samples. [10] Numerous computer methods for identifying the structural parameters of fibrous structures can be found. However, they can only be applied to high-quality samples of products with relatively simple structures and low density. They are useless for samples damaged or partially destroyed due to deformation, burning or milling, as archaeological textiles often are. Another problem is that some fabric parameters, such as yarn crimp, cannot be determined using traditional methods due to unclear fabric cross-section and brittleness of the yarn and fibres.
8.3
Yarn characterization
8.3.1 State of the art The correct and accurate evaluation of yarns is of major importance to the textile industry, as final fabric quality depends directly on yarn quality. Several © Woodhead Publishing Limited, 2010
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companies have developed equipment for testing yarns. The Tester 5 from Uster and the Multitester from Zweigle are notable for their contributions to the development of quantitative yarn characterization. However, these machines are expensive, require a considerable amount of space for installation and present limited resolution and precision for evaluating certain yarn parameters. As a result, some yarn producers do not have their own yarn testing facilities and instead subcontract to dedicated testing laboratories. [11] Yarn can be analysed for different characteristics using image analysis, such as blend characteristics, thickness, diameter, hairiness, number of twists, geometrical dimensions and irregularity. Numerous researchers have introduced different illumination and image processing techniques for yarn characterization. [12] For example, scanning electron microscopy (SEM) can be used to examine the physical characteristics of the fibres in a yarn. SEM allows specimens to be examined without coating and drying, and also permits structural changes in textile materials to be observed under different conditions, such as wetting and heating. [8] Cybulska and colleagues [6, 10, 13] proposed a method for estimating yarn structure using digital image analysis. The yarn’s basic structural parameters, such as thickness, hairiness and twist, are assessed by applying image processing techniques expanded by numerical methods. Numerical structural characteristics are obtained at every point of the yarn length, as well as acceptable average values and dispersion measures for the yarn’s structural parameters. The first stage of analysis is to reconstruct an image of the sample itself, which involves multiplied application of the appropriate filtering and non-linear image transformations to obtain an image that recovers the texture of the fabric. It is necessary to take into account changes in the sample, such as shrinkage and other deformations due to ageing in hazardous environments. Two different methods for yarn modelling are presented. The first consists of forming the yarn from previously created 3D models of fibres by wrapping, twisting or nodding them. The method allows some predetermined features to be set, such as yarn unevenness or hairiness for staple yarns. The second method consists of giving the linear element texture with properties determined by the yarn’s structural properties. The presence of fibres is reflected by concavities and convexities on the cylindrical yarn surface. The method can be used to simplify the first method or as an alternative way to form the virtual yarn. Kopias et al. [14] used image digitization to evaluate pneumatically spliced polyurethane and textured yarns. For image digitization, they applied a method based on a scanner connected to a computer equipped with software programs designed for automatic object recognition. Abnormalities in the automatic image recognition process were eliminated manually. Computer vision techniques have been used for yarn characterization research for more than 20 years. Several studies have been reported using
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computer vision to measure one or more characteristics simultaneously. The commercial testers Uster Tester 4SX and Lawson Hemphill YPT were the first equipped with testing modules with CCD sensors. Computer vision probably provides the widest range of possibilities for hairiness assessment, enabling both simulation of current indices and development of new ones. [12]
8.3.2 Measuring yarn irregularity The production of a yarn is not completely controllable if the amount of fibre in the processes is variable. Moreover, fibres are not regular in shape and geometry, and can be blended with foreign elements. The principal causes of yarn irregularity may be summarized as: [15] ∑ Variations in fibre characteristics ∑ Random arrangements of fibres ∑ Non-random arrangement of fibres caused by faulty production ∑ Irregular twisting ∑ Existence of foreign elements in the fibre. The regularity of a yarn fundamentally depends on the fibres and their arrangement within the yarn. [15] The main sources of yarn irregularity are random fibre arrangement and fibre-length effects, drafting waves, twist variation and foreign elements. [16] Figure 8.3 shows a yarn with thick and thin points. Two methods are commonly used in the textile industry for measuring yarn irregularity, one employing optical sensors to measure irregularity in diameter and the other using capacitive sensors to measure variation in mass. Charge-couple device (CCD) sensors are likely to replace conventional optical sensors owing to their much higher resolution capabilities and versatility. [12] In capacitive measurement, the irregularity of the yarn is detected from variations in electric capacitance generated as the yarn specimen moves through the gap of a fixed air condenser. In photoelectric measurement, the irregularity is measured from fluctuations in light intensity or shadow on the sensor caused by a light beam passing across the yarn cross-section. Table 8.1 compares optical and capacitive methods.
8.3 Thick and thin points in the yarn.
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Table 8.1 Comparison between optical and capacitive methods Method Advantages Disadvantages Optical ∑ Sees like eye ∑ ∑ Suitable for hairiness determination ∑ ∑ More sensitive for diameter variations ∑ The fibre material does not affect ∑ measurement due to conductivity ∑
Discrete sampling causing lower resolution Irregular shape of yarn cross-section Inhomogeneous radiant intensity Sensitive to vibrations during measuring
Capacitive ∑ Continues sampling ∑ ∑ ∑
Sensitive to both temperature and humidity Not suitable for hairiness calculation Sensitive to fibre material
Source: Ref. 16.
One of the early methods used to measure diameter irregularity was to compare the amount of light measured by a photocell before and after insertion of a yarn, the difference being proportional to the diameter. The photocell readings were calibrated using wires with known diameters. This technique was, however, affected by surface hairs, resulting in a significant and inconsistent rise in diameter measurements. [12] Another common method was direct manual measurement of yarn diameter, using magnified images obtained from a microscope or by projecting the shadow on a screen through magnifying lenses. However, this method was not favoured due to its tedious nature. Another approach to determining diameter irregularity is optical filtering. Rodrigues et al. [17] explain that it is possible to separate the hairs from the core yarn using a special filtering mask with coherent dark-field imaging. Chu and Tsai [18] introduced an area compensation method to overcome inhomogeneous light intensity, one of the main restrictions in traditional optical methods that use photoelectric sensors. It is evident that the light and illumination arrangement play an important role in acquiring and pre-processing yarn images. According to the literature, illumination methods for yarn imaging can be categorized in three main groups: back-lit (e.g., Zweigle G565), front-lit (e.g., Cybulska [13]), and dark field (e.g., Uster Tester Hairiness Attachment). Back-lit illumination is the most common method, especially for measuring diameter. [12] The main problem in image processing for yarn irregularity is defining the boundaries between the core and the surrounding hairs. For back-lit and front-lit images, the most common approach is to set a certain threshold value and identify the longest interval of yarn pixels as the core. However, the diameter measured will be strongly affected by this threshold level. In
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addition, when using high resolutions, assuming that the longer duration signals represent the core can sometimes cause hairs lying along the scan line to be identified as the core. At high resolutions, there is also typically no significant change in the intensity of the CCD signal between highly dense surface fibres and the core. This increases the core diameter measurement if a single threshold is applied. Cybulska [13] presented a technique to define core boundaries for front-lit yarn images. The method initially found the core edges from the connected intervals of foreground pixels having the greatest length by scanning each line in the image perpendicular to the core axis. These initial boundaries were then corrected according to some predefined curves along which points generating the edge of the yarn core are assumed to be randomly distributed.
8.3.3 Measuring yarn hairiness Hairiness is the result of fibres escaping from the strand. It is generally desirable to reduce yarn hairiness as much as possible since it causes significant problems in both yarn production and in subsequent textile operations. Such problems include higher friction during spinning, greater fly fibres, and increased yarn breaking during weaving. Yarn production costs need to be minimized while maintaining yarn hairiness and yarn strength within required limits. [19] Measuring yarn hairiness (Fig. 8.4) is traditionally based on microscopic, weighing and photoelectric methods. [20] Image processing methods are still under development, but to classify hairiness accurately, they require a well-defined algorithm to distinguish the hairs from the main core, a camera with a high level of optical magnification and a computer-based system with high computational resources to process results within an acceptable time. These characteristics severely increase the cost. [20]
8.4 Hairiness in the yarn.
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8.3.4 Yarn System Quality (YSQ) Yarn System Quality (YSQ) is presented as an innovative, low-cost, portable and high-precision yarn evaluation tester for quality control of yarn characteristics under laboratory conditions. [11, 20] It has a modular format, which can integrate yarn hairiness, mass, regularity and diameter measurements simultaneously, and enables the determination of some yarn production characteristics. Quantifying yarn hairiness and diameter variation (with a sampling resolution length of 1 mm) is carried out using photodiodes. Diameter characterization, based on samples 0.5 mm wide, uses a linear photodiode array. Measurement of mass variation, based on samples of 1 mm, employs a parallel plate capacitive sensor. In YSQ measurement parameters based on optical sensors, a coherent signal processing technique with Fourier analysis is used to obtain linear and consistent output signal variations, and the measurement systems are automatically calibrated. YSQ introduces new statistical yarn parameters and new signal processing approaches for periodic error analysis, and establishes a reliable method of yarn characterization, as, depending on the resolution used, it is possible to obtain parameters by direct measurement. [20] YSQ is thus a system that reduces equipment costs and offers superior product quality and high production efficiency. In comparison with available commercial systems, YSQ presents several new characteristics. These include the simultaneous use of coherent optical signal processing for characterizing yarn hairiness and diameter; auto-calibration procedures for determining yarn hairiness reference and diameter; direct detection of nep irregularities via integration and measurement of yarn mass variation based on 1 mm capacitive sensors; determining new parameters in yarn analysis allowing highly precise yarn characterization; use of three signal processing techniques; enabling accurate characterization of periodic errors; automatic determination of yarn production characteristics; modular integration of yarn mass measurement, hairiness measurement, diameter variation measurement and precise diameter determination; high portability due to its smaller size; and suitability for yarn quality control use in the laboratory or industry environment. [11, 20]
8.3.5 Computer vision for textured yarn interlacements False-twist textured yarns lack inter-filament cohesion, and consequently a number of difficulties are observed during unwinding and fabric-forming processes. One modern technique for imparting cohesion in false-twist textured yarns is air-intermingling (interlacing). Air-intermingling uses a nozzle to create a very turbulent, high-speed airflow. This creates regular but intermittently entangled nodes in the open structure of the textured yarn, commonly known in the industry as ‘nips’. © Woodhead Publishing Limited, 2010
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The frequency and regularity of nips and their stability under applied loads are important criteria in assessing the performance of mingling nozzles and the quality of the intermingled yarns. A system has been developed that automatically detects nips in yarns with or without applied tension, which can otherwise be seen by the naked eye in the absence of tension. [7] The system is divided into two main parts, the yarn transport section and the yarn imaging/analysis section. [7] For each part, a separate PC is used, but the two are connected. The imaging PC controls all operations, and sends instructions to the transport control PC, which can operate in a stand-alone fashion if necessary. The yarn is imaged using a 1024 pixel line scan CCD camera that scans up to 10 kHz. For a yarn travelling at 10 m/s the scan-to-scan resolution is 1 mm. Two orthogonal views of the yarn in the same cross-sectional plane are used to characterize the yarn. A mirror inclined at 45º to the viewing plane achieves this, as shown in Fig. 8.5. This technique has been shown to provide more accurate evenness data for staple fibre yarns.
8.3.6 Image processing to control nanofibre production Nanotechnology is an emergent technology that is developing quickly and is gaining greater importance in many fields. Nanotechnology can be defined as the science and technology related to understanding and controlling matter at the nanoscale, mainly oriented towards the research and development of materials, devices and systems with novel properties and functions due to their dimensions or components. Nanomaterials are generally characterized as materials with dimensions of 100 nm or less. Electrospinning is a process that creates polymer nanofibres with diameters in the range of nanometres to a few microns. [12] The fibre diameter, structure and physical characteristics Light source Field lens
Yarn CCD camera
45° Mirror
8.5 System to control textured yarn interlace [7].
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of nanofibres can be effectively tailored by controlling various parameters that affect the electrospinning process. [21] Although electrospinning is based on quite simple principles, a lot of work has been done to understand how various parameters influence the process and the characteristics of the resulting nanofibres. Research into electrospinning under different conditions has used SEM to examine different aspects, including fibre diameter, porous fibre surface, arrangement of the fibres, etc. [21] Classical methods of analysis, such as water retention, deliver quantitative information about pore structure, and inverse volume exclusion chromatography provides information about pore size distribution, but neither provides any information on their spatial distribution. [22] Real-time observations of the electrospinning process have been made, using high-speed, high-magnification imaging techniques. Yarns electrospun from polyethylene oxide have been analysed using wide-angle X-ray diffraction (WAXD), optical microscopy, and environmental scanning electron microscopy (ESEM). [23] The internal morphology of the main artificial fibres can be visualized by applying fluorescence and transmission electron microscopy to fibre cross-sections. A more detailed examination of the internal pore structure of fibres can be made by combining information about pore accessibility (from fluorescence microscopy) and the visualized pore structure. [24]
8.3.7 Commercially available yarn characterization testers The following yarn characterization testers are used by yarn manufacturers to evaluate the different properties of yarns. Multitester® from Zweigle Zweigle’s Multitester® consists of three individual modules: ZT 5, OASYS® and G 567. The MT-Multitester can be customized as an individual standalone module or in sets of two or three. This system presents three different sensors to give an all-round picture of sliver, roving and yarn evenness and hairiness. The G 567 Yarn Hairiness Tester measures hairiness using a newly developed optical measuring head with a laser light source, which has an extremely long working life at constant light output. The G 567 covers nine fibre length zones, from 1 mm to 15 mm, in one pass, producing objective, reproducible data. It is controlled by a PC that also analyses the test results. Any desired number of measurements can be made on a bobbin. The G 567 becomes a fully automated tester by adding a bobbin changer with 24-bobbin capacity. The G 567 operates independently. [25]
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The ZT 5 module is an evenness tester with capacitive sensors. For measuring yarns, either measuring channel of the capacitive yarn sensor may be used, depending on the yarn count. For users intending only to test yarns, the sensor on the left, intended for rovings and slivers, may be omitted. [25] The OASYS® module is an optical system for visually assessing yarns in woven and knitted fabrics. The system operates on the principle of absolute optical measurement using infrared light. [26] The structure of a yarn is subject to variations of a periodic or random character. The measuring system compares the yarn diameter with the constant reference mean and records variations in length and diameter. The reference mean is established in the first 100 m of testing. This system uses an infrared light sensor operating with a precision of 1/100 mm over a measuring field length of 2 mm and at a sampling interval also of 2 mm. The speed of measurement may be selected on a graduated scale between 100 and 400 m/min. The sensor is unaffected by ageing of the light source, extraneous light, contamination, temperature or humidity. It is also unaffected by yarn characteristics such as colour, conductivity and lustre. Defects are classified in respect of their length and their variation in diameter. The system provides the coefficient of variation of the diameter values, CV(%), a CV(L) curve, a histogram that shows diameter distribution, and a spectrogram that shows wavelengths of the periodic defects in the yarn. [26] The essential function of the OASYS® system lies in its ability to simulate yarn irregularities on boards and woven and knitted fabrics using previously measured yarn data. Uster Tester 5 The Uster Tester 5 is an offline yarn testing device that has six sensor options and provides a detailed yarn profile in less than 60 seconds. The Uster Tester 5-S800, the most recent design, measures the most important quality parameters, such as evenness and yarn imperfections, with high precision at 800 m/min testing speed. This system uses capacitive and optical sensors, and can determine the evenness, number of thin places, thick places and neps, periodic mass variations, variance–length curve, hairiness, remaining dust and other contaminating particles in yarns, diameter, diameter variation, roundness, density, number of foreign fibres, and count. [27] The Uster Tester 5 apparatus is characterized by: [27] ∑ OH Sensor: hairiness – a perceptive indication of touch and wear ∑ OM Sensor: diameter and shape – advanced prediction of appearance ∑ OI Sensor: accurate measurement of dust and other contaminants ∑ FM Sensor: classification of foreign fibres ∑ KBS: advanced identification of machine defects.
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Keisokki KET-80 and Laserspot The Keisokki KET-80 and Laserspot [16] are two types of evenness tester based on capacitive and optical measurement principles, respectively. Like the Uster Tester, KET-80 provides a U% and a CV(%), a CV(L) curve, and a spectrogram. It also provides a deviation rate, DR%, which is defined as the percentage of the summed-up length of all partial irregularities exceeding the preset cross-sectional level to the test length. In practice, however, the yarn signal is primarily processed by the moving average method for a certain reference length. As a result, long-term irregularities are likely to be detected. The Laserspot evenness and hairiness instrument uses laser light and is based on the Fresnel diffraction principle. With this principle, the yarn core is separated from hairs, allowing yarn diameter and hairiness to be measured at the same time. Flying Laser Spot Scanning System The Flying Laser Spot Scanning System [16] consists of three parts: the sensor head, the specimen feeding device, and the data analysis system. When an object is placed in the scanning area, the flying spot generates a synchronization pulse that triggers the sampling. The width between the edge of the first and last light segments determines the diameter of the yarn. Depending on the spot size and specimen feeding speed, the measurement values may vary, therefore it is important to calibrate the system for the feeding speed and the spot size.
8.4
Special advances in measuring yarn characteristics
8.4.1 Introduction to special advances in measuring yarn characteristics Growing international competition, increasing cost pressure, customer demand for high and consistent product quality, the variety of products and the need to quickly satisfy customer demand make modern and efficient quality control systems extremely important. [26] Quality control should be applied to every process in the textile production line and not just to the finished fabric. The goal is early determination and elimination of faults. One important part of quality control is textile inspection. Fast, continuous quality inspection and the increasing number of fibre materials and applications require modern, efficient test and analytical methods. Quality inspection can be separated into two different fields: [26] ∑
Offline inspection, which is used to check the properties of the finished product (e.g. bobbin) in testing laboratories © Woodhead Publishing Limited, 2010
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Online inspection, which is used to monitor process parameters (e.g. yarn tension, yarn speed) on the production line.
Quality control is related to measuring yarn characteristics, and both methods of quality inspection can involve analysing the yarn at the macro- and micro-level. [26] Special techniques for measuring yarn characteristics have been developed in recent years and applied to analysing yarn structures. Physical characteristics are checked at the macro-level and molecular properties at the micro-level. Figure 8.6 shows the different quality inspection methods for artificial fibres. The methods currently used to measure yarn characteristics include a multiplicity of offline measurement systems which test physical properties as well as molecular structures and morphologies. Online methods are only used for determining physical properties, although using online determinations to obtain information on the molecular structure and morphology would be beneficial. Table 8.2 presents different techniques used to measure the main yarn characteristics at macro- and micro-levels offline. [26]
8.4.2 Yarn quality in the spinning process Yarn production is the first procedure in textile formation. As yarn is the basis for all subsequent procedures, the following yarn properties must be optimized fibre fineness, fibre staple length, yarn strength, elongation, purity and rigidity. [28] During yarn production, yarn characteristics must be quality controlled at the following levels: [28] Measuring of yarn characteristics
Offline
Online
Macro-level
Micro-level
Macro-level
Micro-level
Yarn properties
8.6 Fields of quality inspection methods for man-made fibres.
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Table 8.2 Macro-and micro-level tests Macro-level (offline)
Micro-level (offline)
Yarn count Fibre diameter Yarn evenness Stress–strain behaviour Mechanical crimp Shrinkage behaviour Interlacing of textured and flat filaments
Differential scanning calorimetry (DSC) Scanning electron microscopy (SEM) Birefringence measurement Infrared spectroscopy (IR spectroscopy) Wide angle X-ray scattering (WAXS) Small angle X-ray scattering (SAXS) Near-infrared (NIR spectroscopy) Nuclear magnetic resonance (NMR spectroscopy)
Source: Ref. 26.
∑
∑ ∑ ∑ ∑ ∑ ∑ ∑
Opening, cleaning and blending of raw materials: uniform opening, more detailed opening gradually, continuous formation of new levels during cleaning, appropriate feeding of the material, correct placing of the material for blending Carding: removing neps and very short fibres, making fibres parallel Combing: uniformity of the sliver produced, condition of combs, neps, static electricity, weight of incoming or outgoing sliver Drafting: cylinder diameter, draft, pressure on the rollers Sliver formation: sliver uniformity, draft, twist Spinning: draft, twist, sliver quality and weight, adjustments, yarn uniformity, yarn strength Package preparation: breaks, machine speed, knots Twisting and steaming of the yarn: breaks, twists, single yarn defects, time.
The majority of fabric defects are caused by defects in the yarns. Table 8.3 presents the potential causes of different defects. Yarn defects may be defined as yarn irregularities that can lead to difficulties in subsequent production stages, or to defects in the fabric. These faults can be divided into three main classes: thick points, thin points and neps. [29] Developing electronic imaging capable of predicting the visual quality of woven or knitted fabrics is expected to enhance the quality of yarn and fabric development processes in the textile industry.
8.5
Online systems for measuring yarn quality
8.5.1 State of the art concerning online systems for measuring yarn quality Introducing image analysis techniques in the textile industry could enhance quality through the efficient use of metrology and control. There is a body of research on the online quality control of textile substrates. [15]
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Table 8.3 Potential causes for different types of defects Defect
Potential causes
Spinning defects
Yarn piecing at the ring spinning machine; piecing character – aleatory; Lint in yarn Arraying of fibres flattened and paralleled, adjacent of wound round the yarn Thickening Foreign additions
Yarn including foreign particles
Waste deposition on parts of the spinning machines Improper carding Strand incorrect drafting on ring spinning machine
Corkscrews
Non-correlation of torsion coefficient with yarn application (for high torsion coefficient) Presence in the yarn of thin areas accumulates high torsions
Greasy yarns
Excessive oiling of spinning machine parts Yarn handling with dirty hands (binding)
Wrinkles
Too small division in the drafting assembly Eccentrically disposed arms and cylinders at drafters Improper parameters of humidity and temperature in the working shed
Pilled yarn
Usage of blends with fibres having high differences between their characteristics (length density, length) Worn out parts of spinning machines, producing accentuated yarn frictions Non-correlation of divisions with mean length of processed fibres Microclimate parameters below normal limits
Yarns with adjacent Improper cleaning of fibrous stock during unpacking, foreign particles opening and blending operations Insufficient cleaning of operating parts (especially of card rollers covering) Yarn imperfections Neps Double yarns
Usage of inferior quality raw materials, with a high impurity content Improper technological processing Eccentric up and down cylinders in the drafting assembly Insufficient pressure at upper cylinder level Improper carding presence of a large number of neps in the card web Improper combing Improper technological parameters for spinning preparation operations Improper quality of semi-products (carded silver, drafted silver, top, roving) Simultaneous feeding of two slivers at the ring spinning machine Improper yarn piecing
Source: Ref. 28.
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Online methods are only used for determining physical properties. It would be beneficial if online determination could be used to obtain information on molecular structure and morphology, because physical properties could then be derived from these parameters [26]. Being able to use a measurement system for more than one yarn property would lead to cost reduction in quality control. Computers, microprocessors and online measurement and monitoring of different parameters in the preparatory and spinning processes have become common features of modern spinning machines. Greater emphasis on diversification and manufacturing of yarns for export means that online measurement of evenness and yarn faults is now essential, but it requires expensive instruments and software. [29] According to Suh et al. [30], no commercial system exists for predicting or visualizing fabric qualities directly from yarn diameter or mass measurements taken online. The systems currently available (such as CYROS®, Uster® EXPERT® and OASYS®), visualize yarn and fabric qualities through various types of images created directly from yarn profiles captured from measurement systems. However, these systems are not completely satisfactory due to the way the yarn data are converted to fabric images and because the images often have to be judged visually in the absence of a quantitative measure. Nor do any of the existing systems ‘map’ or ‘fingerprint’ the quality of a woven or knitted fabric for an entire roll or at any specific location within a roll. Therefore, there are no methods for judging and ranking the visual or physical qualities of fabric rolls produced by a given machine at different time points or from different yarns, or from more than one machine. Another unsolved technical issue is defining and measuring the ‘most ideal yarn signals’, whether optical, capacitive, or ‘fused’ opto-capacitive, that best depict the true fabric image. The optical and capacitive methods currently being used are known to be grossly inadequate due to distortion of actual yarn images within a fabric. Suh et al. [30] present a system for electronically imaging the quality attributes (weight, uniformity of appearance, physical properties, etc.) of woven and knitted fabrics directly from an online yarn mass/diameter measurement system without having to go through the actual fabrication processes. They have examined and expanded mathematical theories and the corresponding algorithms for image simulation, data reduction and data mapping onto the structural geometry of woven and knitted fabrics, at both micro- and macro-scales. According to Suh et al. two different yarn profile measurement systems have been developed [16, 30]: ∑
Data fusion: This system comprises measuring, combining and analysing data from multiple sensors. Although data fusion has been implemented in many engineering systems, it has not been widely used in textiles due to the non-linear interaction of multiple inputs to multiple outputs.
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Additionally, different sensors have different sampling rates, precision, accuracy, bandwidth, etc., which makes combining measurements difficult. A line-scan camera and a mass sensor capture yarn data in real time. For each millimetre of yarn, the counter generates a pulse, triggering the camera and the mass sensor. The data from the camera and mass sensor are collected and stored in an array. The size of the array is crosschecked with the location information provided by the counter. A new hardware system that enables input tension and speed to be controlled while simultaneously measuring output tension, yarn diameter (every 1 mm) and capacitance (every 8 mm) has been developed. Multiple yarn diameter measurement: This is a new system for measuring yarn diameters at more than one angle to obtain a better average for the diameter and compute the overall ‘eccentricity index’ of the yarn along the axis. First, assuming the yarn is circular, the yarn is held between the camera and the light source and rotated clockwise in 12 steps each of 30 degrees for a full rotation. At each step, a picture of the yarn diameter is taken to examine the yarn profile. The data are analysed by a Matlab program to produce a cross-sectional image of the yarn. Software has been developed that communicates with the hardware to collect data and store them in a file for further analysis.
Lotka and Jackowski [31] present an online system for analysing the quality parameters of yarns formed in rotor spinning, which is carried out by means of a computer measuring system and pays particular attention to yarn tension. Yarn tension is a phenomenon inseparably connected with spinning, and is also of fundamental importance in rotor yarn formation. The problem of dynamic yarn tension fluctuations is of paramount importance, because they may cause a decrease in yarn quality parameters, such as irregularity of linear density, elongation and tenacity, and therefore an increase in the number of faults. The system allows continual recording of linear density of the yarn, linear density of the sliver and yarn tension. The basic elements of this system are a computer and three measuring heads connected to the computer by means of a measuring interface. The T-measuring head (based on a tensometric gauge) measures yarn tension, and two Uster electro-capacity measuring heads determine irregularities in linear density. Figure 8.7 presents a block schematic of the computer measuring system. The measuring interface consists of an analogue-to-digital converter module, filters, amplifiers, and a voltage supply module. The system is flexible and adaptable to any PC. The software permits the spinning process to be controlled, and visualizes the parameters measured, as well as conducting data capture, processing and retrieving. YSQ (see also Section 8.3.4) represents a low-cost system for determining
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T
Filters and amplifiers
CVy CVS
Computer
A/C converter module
8.7 Block schema of the computer measuring system. T: yarn tension measuring head; CVY: yarn linear density measuring head; CVS: sliver linear density measuring head; A/C: analogue-to-digital converter [32].
Analogue microscope
USB Web camera
PC (NI-Imaq vision)
8.8 YSQ system schematic [20].
yarn production characteristics. The system includes a USB web camera associated with a microscope and using monochromatic illumination. The image processing technique was developed using IMAQ Vision software from National Instruments. The custom application analyses an image source and determines the desired yarn production characteristics, namely, the fibre twist orientation, the twist step and twist orientation in folded yarns, and the number of cables (folded or spun yarn). The system was validated by comparing the results with electron microscope images. [20] It is illustrated in Fig. 8.8.
8.5.2 Commercially available devices for measuring yarn quality Uster solutions Uster Sliverguard® The Uster Sliverguard® is an automatic, modular online system for quality control in sliver production. The system monitors measurement fluctuations, unevenness and periodic faults on the production line directly. As soon as the defined limits are exceeded, an alarm or a machine stop is triggered. This modular online monitoring and auto-levelling system is used in spinning preparation for short staple spinning mills. It is sold as a retrofit sliver monitoring solution for drawframes, combers and cards, and also as an OEM product for monitoring and auto-levelling. The system permits continuous monitoring of all major visible sliver quality parameters: linear mass (A%),
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evenness (CV%, CVL%), periodic faults in spectrogram form, and short thick-places (>1.5 cm length). [27] The conventional offline method of sliver quality monitoring involves checking count and unevenness values, and visually checking the spectrogram only two to three times per shift. This creates problems because only a very short sliver production is supervised (less than 0.02%), the moment a machine fault produces poor sliver quality is not known, thick places in the sliver cannot be captured and, in the case of auto-levelling drawframes, performance is not continuously supervised. [27] The Uster Sliverguard® system can be introduced on drawframe, card and camber machines as a retrofit solution. Uster Quantum 2® The Uster Quantum 2® is considered as a yarn clearer, and is integrated with intelligent advanced sensing technology such as Computer Aided Yarn (CAY) clearing. This system monitors online quality options in a package comprising Uster Quantum Expert®, Uster CAY, true hairiness measurement, vegetable filter, splice classification and Classimat. [27] The system separates critical quality outlier bobbins and quantifies them for the entire production on a continuous basis. Some product highlights include: [27] ∑ ∑
Combination of capacitive basic clearing with foreign fibre clearing Advanced clearing limit optimization using CAY (Computer Aided Yarn) clearing ∑ Detection of foreign fibres at low intensity ∑ Vegetable filter, to filter out vegetable matter that disappears after bleaching ∑ Total testing – quality monitoring of the complete production on the same basis as the Uster Tester and Uster Classimat Quantum ∑ Splice classification per position with CAY ∑ Detection of white and coloured polypropylene. Uster Ring Expert Uster Ring Expert is used for online quality and production monitoring and monitors machine settings, production data and quality data simultaneously. The system monitors each individual spinning position. The information supplied is used for process optimization. It is designed to monitor individual spindles for reliable measurement of end breaks and traveller speed. End break frequency, slipping spindles, production, efficiency and stoppages are systematically monitored. [27]
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Barco solutions BarcoProfile is a system with applications in online yarn quality control on air-jet and friction spinning machines, on winders for technical yarns and also on air-jet texturing machines and in spinning blow-room preparation and ring spinning. Application in rotor spinning machines BarcoProfile, also known as Schlafhorst’s Corolab, is an optical yarn measurement system used on rotor spinning machines. The system measures the yarn diameter for every millimetre of yarn. It can also perform all the above-mentioned open-end (OE) yarn clearer functions, together with detection of foreign fibre material, and allows OE yarn spinners to deliver contamination-free yarn to their customers. [32] The BarcoProfile optical yarn clearer is available for all kinds of OE spinning machines. Apart from the yarn clearer functions, BarcoProfile also substitutes for time-consuming laboratory-based spot checks, because of its built-in 100% online and real-time quality assurance functions. [32] The sensor measures the shadow cast by the yarn on the photoreceiver. State-ofthe-art opto-electronics ensure supreme stability in even the most adverse environments. This allows an absolute measurement and leads to a detector capable of detecting even the faintest gradual diameter changes. Based on the measured diameter values, software algorithms reconstruct and analyse the yarn profile. Positions are stopped based on user-selectable criteria. Application in air-jet texturing BarcoProfile is also used as a quality monitoring system for air-jet texturing. Using conventional opto-electronics, the receiver signals are converted into an absolute and accurate diameter value, which serves as the basis for several types of analysis. [32] The standard measuring accuracy is 0.01 mm, with an optional increase to 0.005 mm. This allows the detection of even the faintest changes in textured yarn diameter. The processed information, together with the most important production data, is sent to a central unit where it is stored in a local database. Via a WindowsCE®-based software interface, the users of the BarcoProfile system get online and real-time information on both textured yarn quality and production. BarcoProfile halts production when something is wrong, and reports on the quality being produced, which positions are approaching off-quality tolerances, and where the exceptions are. [32] The most important analyses performed by the BarcoProfile system are the online calculation of CV%, the thick and thin yarn count channel (for this channel, BarcoProfile makes use
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of the direct correlation between yarn count and measured yarn diameter) and the detection and classification of thick and thin defects. [32]
8.6
Future trends
Image processing techniques are applied to yarn structure to measure some structural and morphological characteristics like irregularity, hairiness, number of twists and yarn appearance. Moreover, image processing is used in special on-line systems to measure yarn quality during the spinning process. In the last few years the rapid evolution in the equipment used for image capturing and analysis has provided an important input for the development of the digital image processing, especially for scientific analysis situations. One of the most important trends that will lead the development of image processing techniques in the near future is the analysis of yarns containing fibres with special structures, like different cross-sections, and functionalities, mainly provided by the incorporation of certain agents during their production steps. The arrangement of these types of fibres in the yarns and their influence on the yarn parameters will result in new achievements in image analysis. Furthermore, techniques for analysing yarns based in micro and, mainly, nanofibers and their on-line quality control are an important future trend. Yarn structure is being customized according to the needs of each particular application, mostly for technical purposes. This trend seems to be one of the most important issues to be faced by image analysis. Besides, it is expected that the advances in informatics and image acquisition and modelling, in general, will contribute positively in this particular area of yarn analysis technique. These advances, combined with image quality and image compression improvements, will be particularly relevant in yarn production environments.
8.7
Sources of further information and advice
The objective of this chapter has been to present, in an integrated and concise form, the imaging techniques applied to yarn structures, and the latest advances in measuring yarn characteristics. For further information the reader should consult more specialized literature, like those suggested below: ∑ ∑
Image Processing and Analysis, Vol. 2, Y.J. Zhang (1999) Introduction to Image Processing and Analysis, John C. Russ and J. Christan Russ, CRC Press (2008) ∑ Adaptive Image Processing: A Computational Intelligence Perspective, K.H. Yap, L. Guan, S.W. Perry and H.S. Wong, 2nd edn, CRC Press (2009) ∑ Image Engineering: Processing, Analysis, and Understanding, Y.J. Zhang, Cengage (2005) © Woodhead Publishing Limited, 2010
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∑
Image Processing and Pattern Recognition: Fundamentals and Techniques, F.Y. Shih, Wiley (2009) ∑ Mathematics of Digital Images, S. Hoggar, Cambridge University Press (2006) ∑ GIS Tutorials: http://www.gisdevelopment.net/tutorials/tuman005.htm ∑ USTER Company: http://www.uster.com/UI/default.aspx ∑ Image processing: http://en.wikipedia.org/wiki/Image_processing
8.8
References
1. GIS Development. The Geospatial Resource Portal; Tutorial: Image Processing and Analysis. Available from http://www.gisdevelopment.net/tutorials/tuman005.htm (accessed 20 November 2008). 2. Castleman, K.R. (1996), Digital Image Processing, Prentice Hall, Upper Saddle River, NJ, pp. 3–5. 3. Drobina, R. and Machnio, M.S. (2006), ‘Application of the image analysis technique for textile identification’, Autex Research Journal, 6(1), 40–47. 4. Awcock, G.W. and Thomas, R. (1996), Applied Image Processing, McGraw-Hill, New York. 5. Song, G., Huang, G. and Ding, X. (2006), ‘Study on automatic stitch length measuring system with digital image processing technique’, Journal of the Textile Institute, 99(5), 415–420. 6. Cybulska, M. (1997), ‘Analysis of warp destruction in the process of weaving using the system for assessment of the yarn structure’, Fibres & Textiles in Eastern Europe, 5(4), 68–72. 7. Millman, M.P. Acar, M. and Jackson, M.R. (2001), ‘Computer vision for textured yarn interlace (nip) measurements at high speeds’, International Journal of Mechatronics, 11, 1025–1038. 8. Zhang, T. (2003), Improvement of Kenaf yarn for apparel applications, Master Thesis, Graduate Faculty of Louisiana State University, Baton Rouge, LA. 9. Xu, B.G., Murrells, C.M. and Tao, X.M. (2008), ‘Automatic measurement and recognition of yarn snarls by digital image and signal processing methods’, Textile Research Journal, 78(5), 439–456. 10. Cybulska, M., Florczak, T. and Maik, J. (2005), ‘Archaeological textiles – Analysis, identification and reconstruction’, 5th World Textile Conference, Autex 2005, 27–29 June 2005, Portorož, Slovenia. 11. Carvalho, V. and Soares, F. (2008), ‘Automatic yarn characterization system,’ IEEE Sensors 2008 Conference, Italy. 12. Ozkaya, Y.A., Acar, M. and Jackson, M.R. (2005), ‘Digital image processing and illumination techniques for yarn characterization’, Loughborough University Mechanical Engineering Department Mechatronics Research Group, Journal of Electronic Imaging, 14(2). 13. Cybulska, M. (1999), ‘Assessing yarn structure with image analysis methods’, Textile Research Journal, 69, 369–373. 14. Kopias, K., Mielicka, F. and Stempien, Z. (1998), ‘An attempt to estimate spliced yarn using computer image analysis’, IMTEX 98 International Scientific Conference, Technical University of Łódz´, Poland.
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15. Castellini, C., Francini, F., Longebardi, G., Tribilli, B. and Sansoni, P. (1996), ‘Online textile quality control using optical Fourier transforms’, Optics and Lasers in Engineering, 24, 19–32. 16. Gunay, M. (2005), Characterization and quantification of woven fabric irregularities using 2-D anisotropy measures, Dissertation submitted for the degree of doctor, fibre and polymer science, North Carolina State University, Raleigh, NC. 17. Rodrigues, F.C. Silva, M. S. and Morgado, C. (1983), ‘The configuration of a textile yarn in the frequency space: A method of measurement of hairiness’, Journal of the Textile Institute, 74(4), 161–169. 18. Chu, W.C. and Tsai, I. (1996), ‘A new photoelectric device for the measurement of yarn diameter and yarn evenness. Part I: Improvement of the variance of radiant intensity using the area compensation method’, Journal of the Textile Institute, 87(3), 484–495. 19. Barella, A. and Manich, A.M. (1997), ‘Yarn hairiness update’, Textile Progress, 26(4), 1–27. 20. Carvalho, V.H. (2008), Automatic yarn characterization system, PhD Thesis, University of Minho, Portugal. 21. Piroi, C., Harpa, R., Cristian, I. and Radu, C. (2007), ‘Electrospinning of polymer nanofibres – Recent developments’, CORTEP Conference, Technical University, Iaşi, Romania. 22. Abu Rous, M., Ingolic, E. and Schuster, K.C. (2005), ‘Visualization of the nanostructure of lyocell and other cellulosics for a basic understanding of their functional and wellness properties’, 5th International Istanbul Textile Conference, Recent Advances and Innovations in Textile and Clothing, Istanbul, May. 23. Deitzel, J.M., Kleinmeyer, J.D., Hirvonen, J.K. and Beck Tan, N.C. (2001), ‘Controlled deposition of electrospun poly(ethylene oxide) fibers’, Polymer, 42(19), 8163–8170. 24. Abu Rous, M., Ingolic, E. and Schuster, K.C. (2005), ‘Revelation of the pore structure of lyocell and other cellulosics applying fluorescence and electron microscopy’, 5th World Textile Conference, Autex 2005, 27–29 June 2005, Portorož, Slovenia. 25. Zweigle Textilprüfmaschinen, available from http://www. Zweigle.com (accessed 18 November 2008). 26. Blascu, V., Grigoriu, A. and Vrinceanu, N. (2007), ‘Some aspects concerning quality control for manmade fibres’, CORTEP Conference, Technical University, Iaşi, Romania. 27. Uster Technologies, Textile Quality Controlling, available from http://www.Uster. com (accessed 18 November 2008). 28. Zampetakis, A., Katsaros, G., Visileanu, E., Vulpe, G. and Niculescu M. (2005), ‘Quality and defect analysis for yarns, knitted, woven fabrics and clothing products’, 5th World Textile Conference, Autex 2005, 27–29 June 2005, Portorož, Slovenia. 29. Chatterjee, S.M., Bhattacharyya, S. and Majumdar, A. (2004), ‘On-line measurement of yarn faults through interfacing with computer’, The Institution of Engineers (India) Journal, Vol. 84, February. 30. Suh, M.W., Jasper, W. and Cherkassky, A. (2003), ‘3-D electronic imaging of fabric qualities by on-line yarn data’, NTC Project, National Textile Center Annual Report, North Carolina State University, Raleigh, NC. 31. Lotka, M. and Jackowski, T. (2003), ‘Yarn tension in the process of rotor spinning’, Autex Research Journal, 3(1), 23–27. 32. BMS Monitoring System, available from http://www.visionbms.com (accessed 2 December 2008). © Woodhead Publishing Limited, 2010
9
Novel technical textile yarns
A. J a l a l U d d i n, Ahsanullah University of Science and Technology, Bangladesh
Abstract: Technical yarns are produced to meet the functional requirements of their intended end-use. With the advent of new technologies, the growing needs of technical yarns in the wake of health and hygiene of consumers are being fulfilled without compromising the issues related to safety, human health and environment. In this chapter, some novel technical yarns such as reflective yarns, UV protected yarns, metal yarns and antimicrobial yarns are described in detail. Moreover, some of the very newly derived technical yarns such as anti-static yarns, anti-stress yarns, anti-allergic yarns, auxetic yarns, shape memory yarns and soluble yarns are briefly introduced. Key words: reflective yarns, UV protective yarns, metal yarns, antimicrobial yarns, anti-static yarns, anti-stress yarns.
9.1
Introduction
The technical textile sector is undergoing fast growth and over the last few years the global technical textile market has moved further into a global commodity market. This change is redefining and accelerating global trade patterns at all levels of the high value chain. The development of technical yarns is the consequence of merging fundamental scientific and technical knowledge, as there is a quest for high performance yarns in a diverse range of applications in different sectors. Thus, constant and continued endeavours of yarn scientists jointly ventured with material technologies have made dreams into reality. These technical yarns provide the potential for providing new applications. This chapter deals with some of these novel yarns and explores the wealth of their properties and applications. Reflective yarns, UV protected yarns, metal yarns and antimicrobial yarns are described in detail. Towards the end of this chapter, some other emerging novel yarns such as anti-static yarns, anti-stress yarns, anti-allergic yarns, auxetic yarns, shape memory yarns and soluble yarns are introduced in brief.
9.2
Reflective yarns
9.2.1 Introduction Reflective materials are commonly seen on tennis shoes, bicycle wheels, road signs, etc. Signs along the roads are visibly enhanced with reflective sheeting 259 © Woodhead Publishing Limited, 2010
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and films. Traffic signs, traffic control devices such as markers, tractor trailer decals and commercial signs would be impossible to see at night without the use of these powerful, reflective materials. They are available in colours such as red, yellow, blue, white, green, orange and many more. Reflective materials can easily be used to make travel safe and easy. Considering the many benefits and advantages of reflective materials in our lives, technology allows reflective materials to come in different shapes and sizes and to meet the needs of any active lifestyle. It offers greater safety outdoors when it is dark by wearing garments of reflective materials. In many situations, the safety features cannot be seen during the day as colours and accents disguise the reflective material. Active wear, sportswear and children’s wear are being enhanced by the safety features of reflective materials. Clothing and accessories in which reflective materials are commonly used include caps, shoes, uniforms, helmets, leg and arm bands, and carrying cases such as backpacks (see Fig. 9.1). Some manufacturers weave reflective yarns into this soft, comfortable fabric to make the ideal clothing for play such as snowboarding and cycling, and work such as police and roadside emergency work. Everyone benefits from the use of reflective materials including children, adults, the elderly, athletes of all types, and even pets.1 Pet products containing reflective materials are becoming increasingly popular due to their safety. Reflective merchandise includes jackets, leashes, shoes, life vests, dog and cat collars and logo wear for pet owners. Fabrics, films, yarns, trims, sheeting and transfers can now be produced with reflective qualities. This means that we can sew or peel-and-stick reflective materials to our clothing, accessories and equipments. Caring for
9.1 Reflective material day/night contrast.
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these materials is also easy as most of them can be machine laundered and ironed on a low setting.
9.2.2 Classification of reflective yarns Reflective yarns can be classified as follows: ∑ Luminescent yarns ∑ Phosphorescent yarns ∑ Prismatico yarns ∑ Retro-reflective or photo-luminescent yarns ∑ Electroluminescent yarns. There have been developments in the field of reflective yarn manufacture. Some of the techniques seem to be very specialized, and are yet to be used in commercial applications. The different companies and researchers have patented their products and have not disclosed the materials or pigments they used in their products. Luminescent yarns Luminescent yarns may be divided into: ∑ Fluorescent yarns ∑ Luminous yarns. Yarns belonging to the fluorescent family are characterized by their intense fluorescent colours. They emit light during exposure to radiation from an external source, i.e., give off luminescence upon receiving light. On the other hand, luminous yarns give off luminescence at night by themselves.2 These fluorescent and luminous yarns can be used separately or in combination to make the portions of woven products or knitted socks or gloves containing such yarns luminous at night or in other conditions of darkness. In this way, the products not only can present luminous beauty but also serve as a warning signal at night.3,4 Scotchlite™ reflective yarns5 are composed of ‘Silver Transfer Film’ laminated (one or two sides) to polyester (1 or 2 mil in thickness) film and slit to narrow widths such as 1/23 inch, 1/32 inch, 1/69 inch, etc. It is also possible to prepare luminescent yarns capable of emitting light of different colours as well as emitting light of a high brightness for a long period of time, whereby these yarns are useful as fibre material for traffic safety and prevention and extinction of fires when applied to yarn for wigs, embroidery and various fabrics. For forgery prevention, fluorescent yarns may be incorporated in producing woven labels and slide fasteners where two or more kinds of fluorescent filaments and similar filaments not containing
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fluorescent substances may be twisted to make special yarns, which are incorporated as warp or filling yarns to show no colour by visible light irradiation, but plural colours by UV and/or IR irradiation for identification of individual information.6 Manufacturing process of fluorescent yarns 1. The synthetic resin is mixed with fluorescent substances having a particle size of 1 to 5 mm (e.g., for emitting blue, BaMg2Al16O27:Eu, for green BaMg2O27:EuMn, for red Y2O2S:Eu, etc.) in the range of 0.2–3 wt% to make luminescent compounds in chip form. These chips are then melt spun and drawn to produce yarn of the required diameter. The synthetic resin is selected from polyamide, polyester, acrylic polymer, polyvinyl acetate, polyvinyl alcohol, polyethylene and polyvinyl chloride. 7–9 2. The fluorescent elastic yarn can also be made with the spin-finish oil containing the fluorescent agent to fluoresce sufficiently to allow a fine elastic yarn to be seen by the naked eye when UV light is irradiated to it.10 Therefore, the fluorescent elastic yarn is advantageous in that core spun yarn (CSY) producers are able to identify its presence inside the hard fibre covering it more easily and timely and to minimize the number of inferior CSY products which are not spun with elastic yarn strands. Phosphorescent yarns Phosphorescent yarns are characterized by their ability to absorb and store the energy of natural sunlight and artificial electric light and slowly emit it in the form of visible light in the dark. The cycle of absorbing, storing and emitting is practically infinite. The afterglow phenomenon is also referred to as phosphorescence and hence these yarns are also known as phosphorescent yarns. For example, Swicofil’s11 new patented phosphorescent filament yarn possesses strong light absorbing–storing–emitting luminescent capability. Swicofil claims that it automatically glows in the dark after absorbing sunlight for 3 minutes or luminous light for 20 minutes. One hour of sunlight exposure would enable this yarn to emit light for up to 3 hours continuously. This light-absorbing process of absorbing–storing–emitting can be repeated indefinitely. Manufacturing process of phosphorescent yarns 1. Phosphorescent glow filament yarns are made by mixing, melting and extruding thermoplastic polymeric chips with photo-luminescent pigments.11–13
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2. Phosphorescent glow yarn may be produced as a two-ply laminated yarn in which a phosphorescent powder has been applied between the two polymer film layers.14,15 3. A wear-resistant, phosphorescent yarn suitable for use in rugs or carpets can be prepared by the application of phosphorescent pigments and light-transmitting natural or synthetic binders to any animal, vegetable or artificial spun yarn during dyeing. Upon dyeing, phosphorescent pigments permanently integrate with the yarn and provide safeguard from abrasion and good wash fastness.16,17 4. The phosphorescence effect may be imparted by immersion of yarns into suitable crystals of activated metallic salts.18 The salts may be ZnS or sulfides of Ca, Sr, Cd, Ba or Mg, the choice depending on the compatibility of these crystal solids in the medium used. Resins that may be used comprise polystyrene, cellulose acetate, polyvinyl, polyethylene, acrylic resins, and copolymers of the same. The crystals are dispersed uniformly over the whole yarn. Such yarns may be used to produce a desired pattern in stockings or in rugs and carpets. Prismatico yarns Prismatico is an effect that is given by a laser-printed pattern on the metallized film. Prismatico is a non-dyeable yarn and may be in both supported and unsupported forms (see Section 9.4.6). It can be produced in silver, gold and other colours. Parameters and photos of prismatico and prismatico 2 ¥ 20 yarns of Ledal Spa19 are given in Table 9.1 and Fig. 9.2, respectively. Retro-reflective or photo-luminescent yarns The production of retro-reflective yarns is very new and innovative. Retroreflective yarn reflects the light, returning it to its source, such as a car’s headlights (see Figs 9.311 and 9.420). These yarns are designed to make the wearer highly visible in daytime, night-time or low-light conditions, especially to increase night-time safety. Joggers, walkers, bicycle riders and highway workers are a few examples of people who benefit from their Table 9.1 Configuration of prismatico yarn
Prismatico
Prismatico 2 ¥ 20
Film thickness Yarn width Composition Yield
25 microns 1/69 inch 100% polyester 65 Nm
25 microns 1/69 inch 78% polyester, 22% polyamide 50 Nm
Source: Ref. 19.
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(a)
(b)
9.2 (a) Prismatico yarn; (b) prismatico 2 ¥ 20 yarn.19
9.3 Retro-reflection of incoming light.11
(a)
9.4 Retro-reflective yarn: reflection.
(b) 20
(a) yarn before reflection; (b) yarn on
use. Retro-reflective yarns can be woven, braided or knitted into fabrics or into trim to be applied to fabric without destroying the aesthetic appearance of the fabric. The driver sitting behind the headlights immediately sees the reflected light and is alerted to the wearer ahead. Other than in safety fields, retro-reflective yarns can be widely used in sportswear and fashion accessories like clothes, shoes, bags and various sorts of leisure goods. During the daytime they appear a beautiful colour and they turn to silver-white at night.
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Manufacturing process of retro-reflective yarns Retro-reflective yarn20–23 consists of fine thermal plastic film to which thousands of micro glass beads and/or pearl beads (bead size 10–50 mm) are bonded with a waterproof flexible resin on both sides, slit to a width as thin as 0.38 mm, then wrapped with nylon fibre to impart strength. The role of the glass beads is to reflect the incoming light to its original light source. This means that the glass beads act as spherical lenses and return the incoming light to the light source when the reflecting layer is set at its focal point (Fig. 9.5). Scotchlite’s retro-reflective yarn Retroglo®21 is made of reflective material having 50,000 minute glass beads to the square inch laminated to a polyester film for added strength. These yarns can be made in sizes of 0.38 mm, 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm and 2.5 mm or could be slit according to the required specification. These yarns combine both aesthetics and technical capabilities to meet the specifications of a wide variety of industrial applications. Retro-reflection
Glass bead Glass bead protective layer Reflective aluminium layer Adhesive layer Back layer
9.5 Retro-reflection principle of glass beads: light strikes the back surface of the beads and returns to its source (adapted from ref. 21).
Electroluminescent (glow-in-the-dark) yarns24 Until now high-visibility clothing has relied on the presence of external light. It absorbs light from its surroundings and then retains a glow for a short time. But on an unlit road, people could be difficult to spot, even if they were wearing safety clothing. In this connection, researchers at the University of Manchester have developed a new battery-powered textile yarn that glows in the dark. The yarns have the potential to be incorporated into clothing worn by cyclists, joggers and pedestrians on dark winter days and nights to improve their safety. The wearer of such clothing can be constantly seen. The development, made from electroluminescent (EL) yarns, emits light when powered by a battery. The yarn consists of an inner conductive core yarn, coated with electroluminescent ink, which emits light when an electric current is passed through it, and a protective transparent encapsulation, with an outer conductive yarn wrapped around it. When the EL yarn is powered,
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9.6 Schematic diagram of electroluminescent yarn.24
the resultant electrical field between the inner and outer conductor causes the electroluminescent coating to emit light (Fig. 9.6). EL yarn can be easily incorporated into a knitted or woven fabric and the resultant active illuminating fabric provides illumination when it is powered. In future the yarn could be used for flexible woven or knitted road safety signs that communicate written instructions.
9.3
UV protected yarns
9.3.1 Introduction Sunlight is the source of all life on earth. Its spectrum extends from about 290 nm to 3000 nm at sea level.25 Small doses of ultraviolet (UV) solar radiation are beneficial to humans, but too much exposure to UV radiation can result in skin damage such as sunburn, premature skin ageing, allergies, and even skin cancer, particularly in white-skinned people. Billions of people live on the earth and each has his or her own colour of the skin. In the human body the skin colour depends on the quantities of melanin, carotene and oxygenated or reduced haemoglobin combined in the skin, as well as the thickness, water content, etc. Among other factors, the quantity of melanin that is distributed in the skin determines its fairness or darkness and greatly
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influences the human complexion, while at the same time melanin plays an important role in minimizing the damage that UV rays cause in the skin. Like visible light, ultraviolet radiation (UVR) is a segment of the electromagnetic spectrum, with a wavelength ranging from 100 to 400 nm, and is conventionally subdivided into three bands: UV-A (320 to 400 nm), UV-B (290 to 320 nm) and UV-C (100 to 290 nm). UV-C is totally absorbed by the atmosphere and does not reach the earth. UV-A causes little visible reaction on the skin but has been shown to decrease the immunological response of skin cells. UV-B is the range of UV radiation most responsible for the development of skin cancers.26,27 Skin cancer is the most prevalent form of cancer and its incidence has been steadily increasing over the past 20 years. This is most probably due to the change is lifestyles in the late twentieth century when sunbathing and tanning became cosmetically desirable. Moreover, excessive exposure to sunlight during leisure activities, for example playing outdoors and swimming in the case of children, and golfing and fishing in the case of adults, has increased the risk of skin cancer. For agricultural and other outdoor workers, exposure to the sun is an occupational hazard as they have no choice about the duration of their exposure. Furthermore, a steady decrease of stratospheric ozone has been observed during the last few decades.28 Since ozone is a very effective UV absorber in the UV-B region, this has led to increased UV radiation reaching the earth’s surface and has thus enlarged the risks of the negative effects of sunlight. Recognizing these facts, it is clearly very important to protect skin (and eyes) from excessive amounts of UV radiation. This can be done by using sunscreen lotions, hats and sunglasses or by wearing protective clothing (UV cutting). The protection that a sunscreen offers depends among other things on the thickness of the sunscreen lotion layer, as well as the concentrations and spectra of UV absorbers in the sunscreen. The recommendation of textiles as a means of sun protection has previously been underrated, even though suitable clothing offers simple and effective protection against the sun. Nevertheless, several studies have recently shown that, contrary to popular opinion, some textiles provide only limited UV protection. 29
9.3.2 Sun protection factor (SPF) The degree of protection that a certain sunscreen lotion or piece of clothing offers against the negative effects of sunlight is commonly described in terms of a so-called ‘sun protection factor’ (SPF).25 In principle, every sunscreen is characterized by a set of SPFs: i.e., an SPF for sunburn, an SPF for skin cancer, etc. For obvious reasons, only precise SPFs for sunburn can be determined for humans. SPF numbers on a package can range from as low as 2 to as high as 60. These numbers refer to the product’s ability to screen or block
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out the sun’s burning rays. The SPF rating is calculated by comparing the amount of time needed to produce a sunburn on protected skin to the amount of time needed to cause a sunburn on unprotected skin.25,29 For instance, for a fair-skinned person who would normally turn red after 10 minutes in the sun, 10 minutes is his ‘initial burning time’. If that person uses a sunscreen with SPF 2, it takes 20 minutes in the sun for that person’s skin to turn red. Now, if that person uses a sunscreen with SPF 15, this multiplies the initial burning time by 15, so it takes 150 minutes, or 2 12 hours, for that person’s skin to turn red. Sunscreens with an SPF of 15 or higher are generally thought to provide useful protection from the sun’s harmful rays. It was found that one-third of commercial summer clothing items provided a sun protection factor (SPF) of less than 15.30,31 Thin, untreated fabric made from cotton, silk, polyamide and polyacrylonitrile offer an SPF in the range of only 3 to 5, i.e., their UV-cutting effect is inadequate when the sun’s irradiation is intense.32
9.3.3 Ultraviolet protection factor (UPF) ‘Ultraviolet protection factor’ (UPF) is the scientific term used to indicate the amount of ultraviolet (UV) protection provided to skin by fabric. UPF values are analogous to SPF values, the only distinction being that SPF values for sunscreens are determined through human testing whereas UPF values are based on instrumental measurements.33 UPF is defined as the ratio of the average effective UV irradiance calculated for unprotected skin to the average UV irradiance calculated for skin protected by the test fabric. The higher the value, the longer a person can stay in the sun until the area of skin under the fabric becomes red.33,34 The Australian/New Zealand Standard (AS/NZS)34 was the first normative publication offering test methods to be used for determining UPF and a classification scheme. Clothing with UV protection ratings has been available in Australia for several years, particularly recreational wear such as beachwear and elastane bodysuits for small children. A worldwide effort has been under way to study factors that affect the UV protection provided by clothing. Radiometric UV transmission tests use a broadband UV light source filtered for UV-B or combined UV-A and UV-B spectral regions to illuminate a fabric sample. The total UV transmission through the textile is measured by a radiometer. For correct measurement, this test method requires a UV source that closely matches the solar spectrum, with detectors that respond similarly to human skin. Nevertheless, this technique is simple and suitable when a relative variation in UPF needs to be measured. Spectroradiometers or spectrophotometers collect transmitted and scattered radiation with the aid of an integrating sphere positioned behind a textile sample. Although spectrophotometers fitted with a double monochromator
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have a large dynamic range and high accuracy, regular scans of the UV source (deuterium or xenon arc lamp) are required to provide reference data. 35,36 As suggested by the AS/NZS 37 and European standard, 38 the spectrophotometer should be fitted with a UV radiation transmitting filter for wavelengths of less than 400 nm (UG-11 filter; Schott, Mainz, Germany) to minimize errors caused by fluorescence from whitening agents. The spectrophotometric measurements are performed in the wavelength range of 290 to 400 nm, in 5 nm steps or less. For UPF determination, at least four textile samples must be taken from a garment, two in the machine direction and two in the cross-machine direction. To determine the in vitro UPF, the spectral irradiance (of the source and transmitted spectrum) is weighted against the erythemal action spectrum, as follows:39,40 400
UPF =
Ú290 400
El Sl dl
9.1
Ú290 where l is the wavelength in nm, El is the relative erythemal spectral effectiveness (this parameter takes into account the human skin response), Sl is the solar spectral irradiance of the source in watts per square metre (this parameter takes into account the strength of the summer sun at noon), dl is the bandwidth in nanometres and Tl is the spectral transmission of the sample. The integrals (Ú) are calculated over the wavelength range of 290 to 400 nm. UPFs of 50 and higher are only of theoretical interest, as even in Australia the maximum daily UV exposure is about 35 minimal erythema doses (MEDs). Ultraviolet transmission measurements of textiles are generally made under worst-case conditions, with collimated radiation at right angles to the fabric. Thus, the actual UV protection of a particular textile would always be greater than the measurement obtained using spectrophotometry. El Sl Tl dl
9.3.4 Standard UPF for UV protective clothing The AS/NZS 439935 and Standards Australia Committee TX/2140 set requirements for determining and labelling the UPF of sun-protective textiles and other items that are worn in close proximity to the skin. According to them, UPFs are classified as shown in Table 9.2. Here it is seen that the objective is to achieve factors between 30 and 50 or more. Textiles with a UPF of less than 15 are not labelled.
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Table 9.2 Classification of textiles by UPF UPF range Classification
UV radiation transmittance, %
UPF labelling
15–24 25–39 40–50, 50+
6.7–4.2 4.1–2.6 <2.5
15, 20 25, 30, 35 40, 45, 50, 50+
Good protection Very good protection Excellent protection
Source: Refs 35 and 40.
and thickness as well as dyes present in the fabric and finishing treatment applied on it. With wear and use, several factors can alter the UV protective properties of a textile, including stretch, wetness, and degradation due to laundering.32 As the present topic is to discuss UV-protected yarns or fibres, our discussion will focus mainly on UV-protected fibres and yarns and the dyeing or finishing treatments applied to them. Summer clothing is usually made of cotton, viscose, rayon, linen, polyester or combinations thereof. Other types of materials, such as nylon or elastane, are also found in bathing suits, stockings and other garments. Consumers generally consider lightweight non-synthetic fabrics (cotton and linen) to be the most comfortable for summer wear. Comparison of the UPF of different types of material is difficult and possible only in limited situations. This is because certain production steps (dyeing and finishing) vary based on the material, resulting in a comparison of the ‘material–colour–finish’ combination and not of the material itself. In the case of synthetic fibres, such as polyester and polyamide, an analysis is even more difficult because the UV protection of these materials depends on the type and quantity of additives to the fibre, such as optical brighteners, antioxidants or UV stabilizers. In accordance with most studies,41–44 the type of fibre used to construct a textile can have a substantial effect on the UPF, especially for white and non-dyed fabrics. Bleached cotton, viscose rayon and even silk are transparent to UV radiation and thus provide relatively low UV protection.42 Compared with bleached textiles, unbleached fabrics such as cotton and silk have better UV-protective properties due to UV-absorbing natural pigments and other impurities. Polyester usually has good UV-blocking properties, as this fabric allows relatively little UV-B transmission, probably because of the large conjugated system of polymer chains.41,42 Polyester (or polyester blend) yarns may be the most suitable for UV-protective garments (Table 9.3). However, its permeability for wavelengths in the UV-A range is frequently higher than that of other fibre types; this could be of significance for wearers with polymorphic light eruption, solar urticaria, chronic actinic dermatitis, or actinic prurigo (Table 9.4).
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Table 9.3 Summary of factors significantly affecting the UPF of apparel textiles Textile material
Fabric porosity Textile colour Stretch Wetness
Washing
UPFs of cotton, viscose, rayon and linen are usually smaller than UPFs of nylon, wool and silk; polyester provides usually high UPFs UPF increases with decreasing yarn-to-yarn spaces and weight, thickness increasing fabric weight and thickness Dark colours provide higher UPF due to increased UV absorption Stretching a textile causes an increase in fabric porosity, with a consequent decrease in UPF UPF decreases dramatically when textile gets wet. The presence of water in the interstices of a fabric reduces optical scattering effects and hence increases UV transmission of the textile. Wet cotton can lose up to 50% of its UPF because water reduces the scattering of UVR, thereby increasing its transmission of harmful ultraviolet rays Most textiles, especially fabrics, undergo a combination of relaxation and consolidation shrinkage when washed. Thus, the spaces between the yarns decrease and UV protection increases
Source: Ref. 32.
Table 9.4 General recommendations concerning UV protective clothing for patients with photosensitivity ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑
Clothing labelled as UV protective,11,14 with a UPF of at least 30, is preferred. The less transparent a fabric is to visible light, the better the UV protection is. The darker the colour of the fabric, the better the UV protection is. Polyester or polyester blends usually offer better UV protection. Stretch and wetness of cotton fabrics significantly decrease their UPF. Looser fits are preferable; the garment should cover the skin as much as possible. New clothing, especially cotton fabrics, should be washed before wearing; special laundry detergents and fabric conditioners may be used that include broadband UV protective absorbers. Despite a high UPF, a fabric’s UV-A transmission can be significant.
Source: Ref. 32.
9.3.6 Preparation of UV-protective yarn The unfinished textile has the limitation of not guaranteeing adequate protection against UV radiation. Moreover, UV radiation and all wavelengths of light, even visible light, weather and degrade the textiles. Consequently, UV-blocking agents have been developed to add to or improve the UVprotective function of textiles.
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Organic and inorganic blockers There are both organic and inorganic blockers. The organic blockers are also called UV absorbers because they mainly absorb UV rays. Molecules of UV absorbers, such as benzotriazole and phenyl benzotriazole, are able to absorb the damaging UV rays of sunlight. UV absorbers convert UV energy into harmless heat energy. This transformation is regenerative and can be repeated indefinitely. Inorganic UV blockers are usually semiconductor oxides such as TiO2, ZnO, SiO2 and Al2O3. Compared with the existing organic UV absorbers, the inorganic UV agents are preferred because of their unique features such as non-toxicity and chemical stability under both high temperature and UVray exposure. Titanium dioxide (TiO2) has good UV-blocking power and is very attractive in practical applications due to its non-toxicity, chemical stability at high temperarure, and permanent stability under UV exposure. Development of nano-science and nano-technology provides new ways for better treatment for UV-resistant yarns, films and fabrics using TiO2.27 Textile dyes Dyes are selective absorbers of visible light. Most dyes absorb light in the region between 400 and 700 nm, and some also absorb light in the near ultraviolet region.45 Deep dyed fabrics or dark colours, especially black and blue, show excellent protection from UV radiation. Other chromatic colours, such as red, yellow and green, also offer very good protection against UV radiation.46 This fact and the possibility of UV light absorption in the short UV region are probably the consequence of the formation of bonds between dye molecules and between dye molecules and fibres. In a study of identical fabrics, it was found that white cotton fabrics had a UPF of 12, whereas a similarly constructed black fabric had a UPF of 32. In testing polyester, studies showed that a white polyester was a 16 UPF and black polyester was a 34 UPF. The popular view that white is more sun-protective than dark colours is erroneous.47 Disperse dyes are used for dyeing polyester fibres. Disperse dyes for these applications are usually azo, anthraquinone and methine. Molecules of disperse dyes have a very low water solubility, and they have polar groups but no ionic groups in their structures. Polyester, an aromatic polyethylene terephthalate, which is highly hydrophobic, is known to have a high protective factor against UV radiation. The influence of disperse dyes on the UPF of fabrics is high. The structure of dye molecules plays an important role. Besides the transmittance and reflectance of UV radiation, the absorbance of UV radiation by molecules becomes important. A UV absorber can also be applied during fibre manufacturing. Application
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of UV absorbers or UV blockers in the yarns significantly improves the UV-protection factor of a garment.32
9.3.7 Technological options to apply UV absorbers on textiles UV absorbers incorporated in dyeing decrease the dye uptake, except in post-treatment application. They are compatible with dyes and are applied by normal padding, exhaust, pad thermosol and pad dry cure methods. The main limitations of UV absorbers are that they cannot be applied in a single bath along with other finishing agents. Anything in excess will have a detrimental effect on the fabric. With the advent of nano-science and nano-technology, a new area has developed in the area of textile finishing called nano-finishing. Growing awareness of health and hygiene has increased the demand for UV-protective textiles. Coating the surface of textiles and clothing with nano-particles is a new approach to producing highly active surfaces with UV blocking properties. Zinc oxide (ZnO) nano-particles embedded in polymer matrices such as soluble starch are a good example of functional nanostructures with potential for applications such as UV protection. Metal oxides such as ZnO as a UV blocker are more stable than organic UV blocking agents. Hence nano-ZnO will enhance the UV blocking property due to its increased surface area and intense absorption in the UV region.
9.4
Metallic and metalloplastic yarns
9.4.1 Introduction Metallic fibres have made the saying ‘spinning straw into gold’ come to pass. Though straw is never used, its place is rightly taken by other precious metals like silver. Metallic fibres are also known as Zari, particularly in India. Metallic yarns or threads such as gold and silver have been used since ancient times as decoration in the clothing and textiles of kings, leaders, nobility and people of status. Many of these elegant textiles can be found in museums around the world. Metallic fibres were the first artificial fibres, created thousands of years before nylon or rayon. Historically, the metallic thread was constructed by wrapping a metal strip around a fibre core (cotton or silk), often in such a way as to reveal the colour of the fibre core to enhance the visual quality of the decoration. Ancient textiles and clothing woven from wholly or partly gold threads is sometimes referred to as Cloth of Gold. It was woven on Byzantine looms from the seventh to the ninth centuries and from then on in Sicily, Cyprus, Luca and Venice.48 Weaving also flourished in the twelfth century during the legacy of Genghis Khan
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when art and trade flourished under Mongol rule in China and some Middle Eastern areas. The Dobeckmum Company produced the first modern metallic fibre in 1946. In the past, aluminium has always been used as the base in a metallic fibre. More recently stainless steel has become an alternative base. It is more difficult to work with but provides properties to the yarn that allows it to be used in more high-tech applications.
9.4.2 Metallic fibres or yarns The term metallic fibre, in its general sense, means simply a fibre that is made from metal. The generic term ‘metallic’ was adopted by the US Federal Trade Commission and is defined as a manufactured fibre composed of metal, plastic-coated metal, metal-coated plastic, or a core completely covered by metal. Thus, metallic fibres are fibres produced from metals, which may be alone or in conjunction with other substances.49 These metal filaments were made by beating soft metals and alloys, such as gold, silver, copper and bronze, into thin sheets, and then cutting the sheets into narrow ribbon-like filaments. The filaments were used entirely for decorative purposes, providing a glitter and sparkle that could not be achieved by other means. As textile yarns, these metal filaments had inherent shortcomings which restricted their use. They were expensive to produce; they tended to be inflexible and stiff, and the ribbon-like cross-section provided cutting edges that made for a harsh, rough handle; they were troublesome to knit or weave, and they had only a limited resistance to abrasion. Apart from gold, the metals would tend to tarnish, the sparkle being dimmed with the passage of time. The filaments are weak and inextensible, and are easily broken during wear; they lack the flexibility that is essential in a genuine textile fibre. Despite these shortcomings, the metallic ribbon-filament has remained in use for decorative purposes right up to the present day. The development of modern techniques of surface-protection has brought cheaper metals into use; aluminium foil, for example, may be anodized and dyed before being slit into filaments which are colourful and corrosion-resistant. More recently, aluminium yarns, aluminized plastic yarns and aluminized nylon yarns have replaced gold and silver. Metallic filaments can be coated with transparent films to minimize tarnishing. A common film is Lurex polyester. In recent years, the ribbon filament of metal has undergone a transformation and the new term ‘metalloplastic’ has appeared. The metal of the filament is now sandwiched between layers of plastic, which protect the metal from the atmosphere and from other corrosive influences. The metal yarns produced by slitting sandwich materials of this type are stronger and more robust than the filaments cut from metal foil alone. They retain the glitter of the metal during prolonged periods of use, and have a soft, pleasant handle. Coloured
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pigments may be added to the adhesive used in sticking the plastic films to the metal foil or metallized film. Metal yarns of this type are now widely used in the textile industry, and are produced in a range of colours and forms by many manufacturers. They remain, however, essentially decorative materials and their applications are restricted to this type of use.
9.4.3 Metal fibre structure Due to its history as a wire-drawn product and its abnormally high specific gravity, metal fibre sizes are typically described in terms of their actual diameter in microns as opposed to their linear weight in denier. Nowadays different companies in the market manufacture very thin metal fibres. Bekaert Fibre Technologies (BFT)50 develops, manufactures and markets very thin metal fibres and metal fibre based products. These metal fibres, in the thickness range of 1 to 80 mm, are up to 60 times thinner than human hair and are available in various alloys. Most textile applications utilize fibres in the range of 8 to 14 microns. By comparison with polyester, a 12-micron metal fibre has the same diameter as a 1.4 denier polyester fibre.
9.4.4 Metal fibre/yarn properties Electrical conductivity Biomedical clothing and conductive textiles, also referred to as smart textiles and e-textiles, have in the last decade been of increasing research interest. Conductive textiles that can avoid electrostatic discharge are desirable not only in home textiles, military applications (e.g. monitoring of physiological parameters), electrical and electronic devices and subsystems, but also in clean-room applications such as in the pharmaceutical and optical industries. The possibility of knitting or weaving conductive yarns into electrodes, integrating the latter into comfortable clothing, makes them particularly usable in situations such as long-term monitoring and home healthcare. Metal yarn has excellent and permanent electrical conductivity among all conductive fibres and moreover is not influenced by environmental humidity. But the contact of metal fibres with human skin makes people uncomfortable. This situation has been avoided by producing metal composite yarn by blending metal fibres with natural or synthetic fibres, or making core-spun yarns or wrapped yarns or braided yarns. Metallic fibres incorporated into these fabrics act as conductive fillers to promote the electrostatic discharge properties of fabric. Other than electrical conductivity, fabrics made of metallic composite yarns possess good cut resistance, abrasion resistance, anti-electrostatic and anti-wear properties.51 © Woodhead Publishing Limited, 2010
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The above-mentioned metallic composite yarn may be used at 100% content in manufacturing knitted or woven fabric or, to reduce cost, may be inserted into fabric at regular intervals with normal yarn. For example, every tenth warp yarn and every tenth filling yarn might make a plain woven fabric, or every tenth feeder might possess such a metallic composite yarn in knitting.52 Electromagnetic shielding Apart from the aforementioned properties, the high electrical conductivity of metallic yarns also leads to excellent electromagnetic shielding characteristics.53 It was found that a fabric comprising yarns containing 73% polyester fibres and 27% stainless steel fibres gave 95–98% shielding against waves and was suitable for protection of the human body from such waves.54 Stainless steel fibres have thus long been utilized as an additive to plastic casings as a way to shield internal components from electromagnetic radiation. As concerns around electromagnetic interference (EMI) shielding grow, these conductive plastic applications have expanded the variety of textile applications for metal fibres. Garments, seals, gaskets and wall-coverings are all commercial application areas for shielding fabrics. There is even ongoing research into the possible therapeutic value of such fabrics for various medical treatments. Heat resistance with superior mechanical properties Since the early 1990s a growing market segment for solid metal fibres has developed in the area of industrial, heat-resistant textiles. A heat-resistant garment has an outer surface mainly comprising metal fibres to provide heat resistance against contact heat. Heat-resistant garments can be used to provide protection against contact heat to the person, animal or object on which the heat-resistant garment is worn.55 As well as high tensile strength, yet another important attribute of metal fibres is the ability of certain metals to behave in a chemically inert way, regardless of the environment that they are exposed to. Stainless steel metal fibres are highly heat-, corrosion- and acid-resistant.56 Lier Filter Technology Co. Ltd57 has made sintered metal fibre felt that is composed of steel fibre mesh sintered together (Fig. 9.7). It still has features of web and porous construction, high strength and high stability in a hightemperature vacuum oven. These advantages make it an ideal material for heat resistance, corrosion resistance and high precision. These high quality filters are ideal for liquid filtration and gas filter applications. Geotextiles are frequently utilized as replacements for other conventional construction materials as they can improve construction quality and speed. The materials commonly used in geotextiles are polyester, polyethylene,
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9.7 Sintered metal fibre felt.57
polypropylene and polyvinyl chloride. Because of its superior mechanical properties, metallic fibre, especially stainless steel, is a new addition in the reinforcement of geotextiles, to make geogrids. Geogrids are composite yarns made of metal and other synthetic yarns. In an analysis, it was found that over a test time of 100,000 hours, the geogrids retained their strength. Chen et al.58 produced geogrids with functional stainless steel/polypropylene composite yarns by braiding. These braided metal composites have potential in the aerospace and automotive industries and in other applications also, due to their low cost and excellent mechanical properties. The relationship between fibre and concrete is significant. In ancient times, people mixed straw into mud to strengthen their houses. With technological advances, concrete replaced mud, and various fibres replaced straw. Reinforced concrete is an extremely common construction material for buildings. Recently various scientists have used metallic fibres such as stainless steel and iron fibres for concrete reinforcement and have reported good results in preventing cracking.59
9.4.5 Metallic yarn manufacturing processes There are two basic processes that are used in manufacturing metallic fibres. Laminating process The most common is the laminating process, which seals a layer of aluminium between two layers of acetate or polyester film. These fibres are then cut into lengthwise strips for yarns and wound onto bobbins. The metal can be
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coloured and sealed in a clear film, or the adhesive can be coloured, or the film can be coloured before the laminating process. There are many different variations of colour and finish that can be made in metallic fibres, producing a wide range of effects. Metallizing process Metallic fibres can also be made by using the metallizing process. This process involves heating the metal until it vaporizes, then depositing it at high pressure onto the polyester film. This process produces thinner, more flexible, more durable and more comfortable fibres.48 In aluminized fabric, aluminium molecules are deposited on a PET film. Examples are Mylar from DuPont and Hostaphana from Hoechst. The aluminized film can reflect up to 90% of radiant heat. Gold can be used for reflection of up to 100%, though it is expensive. Along with various kinds of metallic fibres, Oike & Co. Japan60 produces gold and platinum thread by vapour deposition of genuine precious metals onto a fibre core. Their gold and platinum thread is used in the production of the most dazzling and magnificent traditional Japanese fabrics such as for kimono and other aristocratic dress materials.
9.4.6 Forms of metallic fibres Metallic fibres may be either unsupported or supported. Unsupported metallic yarns Metallic yarns start as rolls of films or laminations 30 inches or wider in thicknesses between 12 mil and 1 12 mil. These wide rolls are slit into narrow rolls 2 to 5 inches wide. These narrow rolls are gang-slit across their whole width to micro widths from 1/128 inch (0.0078 inch) and wider and then taken up on plastic spools for shipment to textile mills.61 Supported metallic yarns Metallic yarns may also be made by twisting a strip of metal around a natural or artificial core yarn, producing a metal surface. It is made of thin film and supported by nylon or polyester or rayon yarn according to the type of yarn. Metlon’s62 supported yarns are made by wrapping single slit metallic yarns with two ends of nylon. One end of the nylon is wrapped clockwise and the other end is wrapped counterclockwise around the metallic yarn. Each nylon yarn has from 5 to 7 wraps to the inch. The most commonly © Woodhead Publishing Limited, 2010
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used nylon is either 15 denier or 20 denier, but heavier deniers are used for special purposes. Supported yarns are put up on cones.
9.4.7 Manufacturing metallic composite yarns There are various ways to produce composite metallic yarns with other textile fibres to make mainly conductive textiles. Core-spun yarns Metallic composite yarns can be prepared by making core-spun yarns in a ring-, rotor- or friction spinning system where the general staple fibres cover the metallic yarn, such as stainless steel or copper wire, and let the metals form in the centre of the core of yarn.63 The manufacturing principles of core-spun yarns in the above-mentioned spinning system are not new and are available in books. Wrapped yarns Metallic composite yarns can be made by making wrapped yarn on a rotor twister in which general yarns, sometimes together with metallic yarn, are placed in the yarn core and wrapped by metallic yarn. Chen et al.64 devised a novel method to produce metallic conductive yarn. Figure 9.8 displays the working principle of the rotor twister. A large package of metal yarn is placed onto the rotor twister device, which is driven by a tangential belt from the motor. The single or multiple core yarns (Fig. 9.8 shows one core yarn) are continuously delivered by the feed rollers towards the rotor twister through a collector. Metallic yarn is also fed into Metallic yarn Collector
Rotor twister
Feed rollers
Core yarn
take-up roller
9.8 Sketch of a rotor twister (adapted from ref. 64).
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the rotor twister together with core yarn and both yarns are twisted when the rotor is rotated. Adjusting the rotation of the rotor twister and the speed of yarn delivery can change the twist amount. After twisting, the hybrid yarn is wound in a winding roller. The internal construction of the rotor-twisting device is hollow, and its inner wall is made smooth during manufacture to avoid friction between the yarn and the inner wall with increasing twisting speed. Fibre blending Blending of staple metallic fibres such as stainless steel staple fibres and general staple fibres can be carried out in a drawframe and the yarn can be spun on the usual ring- or rotor-spinning system in the same way that polyester–cotton (PC) blended yarns are produced in the conventional cotton spinning system.65 Braid Metallic composite yarns can be made by making a rope-like braid of metallic and general yarns, such as stainless steel and polypropylene yarns, in a braiding machine.66 Braiding is one of the major fabrication methods for composite reinforcement structures.
9.4.8 Metallic yarn uses Metallic yarns have an innate memory feature. They offer a touch of class that will bring back the old days when pure silver and pure gold threads were used to ennoble past collections. The most common end-use for metallic fibres is for upholstery fabric and textiles such as lamé and brocade. Lamés are most commonly made of a polyester jacket, overlain with a thin, interwoven metal, usually steel or copper, which gives them a metallic greyish look. This apparel is popularly used in fencing. Brocade is the special fabric in which coloured silk is used woven with silver and gold threads. This exquisite fabric is in great demand throughout the Middle East and Asia. Many people also use metallic fibres in weaving and needlepoint. Stainless steel and other metal fibres are used in communication lines such as telephone lines and cable television lines. Stainless steel fibres are also used in carpets. They are dispersed throughout the carpet with other fibres so that they are not detected. The presence of the fibres helps to conduct electricity so that the static shock is reduced. These types of carpets are often used in high-volume computer areas where the chance of producing static is much greater. At one time or another, metallic yarns have been used in just about every
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form of textiles. Some end-uses have been in automotive fabrics, television front fabrics, bath towels and face cloths, clerical vestments, bathing suits, hosiery, upholstery, hat bands, theatrical clothing, theatre backdrops, doll’s clothing, banners, uniforms, etc. Other uses of metallic fibre include tyre cord, missile nose cone, work clothing such as protective suits, space suits, and cut-resistant gloves for butchers and other people working near bladed or dangerous machinery.
9.4.9 Applications in technical textiles The possibilities for various applications of metallic fibres/yarns are enormous. The following is a short overview on the numerous areas of usage:67 ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑
Anti-static protective clothing in the petrochemical industry, pilot suits, fire workers’ suits, etc. Sound absorbers in all kinds of silencers Raw material for brakes, friction and clutch linings Filter material for mechanical and magnetic filters Basis material for sinter products, compounds and conductive plastics Support material for thermal and electrical processes Shielding against radiation, i.e., shielding fabrics for utility workers in high field areas Muscle stimulation electrodes Electrostatic discharge (ESD) brushes Bulk container bags for powders and pellets.
9.4.10 Care of fabrics with metallic yarns Professional dry cleaning with perchlorethylene is preferred to laundering. Hand laundering with Woolite and cold water is the only suggested laundering method. Metallic yarns must never be laundered with bleach. Fabrics containing metallic yarns should be treated like all synthetic fabrics. Ironing should be at the lowest setting on the iron. If there is no thermostat on the iron, it is advised not to use that iron. Steam should not be used when ironing metallic yarns.
9.4.11 Producers The Lurex Co. Ltd has manufactured metallic fibres in Europe for over 50 years. They produce a wide variety of metallic fibre products including fibres used in apparel fabric, embroidery, braids, knitting, military regalia, trimmings, ropes, cords and lace surface decoration. The majority of Lurex fibres have a polyamide film covering the metal strand, but polyester and viscose are also used. © Woodhead Publishing Limited, 2010
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Currently metallic fibres are manufactured primarily in Europe with only three manufacturers still producing metallic yarn in the United States. Metlon Corporation is one of the remaining manufacturers in the US that stocks a wide variety of laminated and non-laminated metallic yarns.
9.5
Antimicrobial yarns
9.5.1 Introduction Micro-organisms or microbes are microscopic organisms that are usually too small to be seen by the naked eye. Microbes are very diverse: they include a variety of micro-organisms like bacteria, fungi, algae and viruses. Textile fibres and the structure and chemical processes of textile substrates provide room for the growth of micro-organisms, especially in suitable conditions of humidity and the warm environment in contact with the human body. The growth of microbes on textiles during use and storage negatively affects the textiles and causes potential health risks to the wearer68 (see Fig. 9.9). Among microbes, bacteria are unicellular organisms which grow very rapidly under warmth and moisture. Fungi, moulds or mildew are complex organisms with a slow growth rate. They stain the fabric and degrade its performance properties. Algae are typical micro-organisms that may be either fungal or bacterial. Algae grow in continuous sources of water and sunlight and develop darker stains on fabrics. Dust mites are eight-legged creatures that feed on human skin cells and liberate waste products that can cause allergic reactions and respiratory disorders. They live in household textiles such as blankets, beds, pillows, mattresses and carpets. Microbial infestation poses dangers to both living and non-living matter. Hospital and healthcare systems are challenged by the presence of microorganisms. Most significantly, these places can act as microbial harbours and Microbial attack
Detrimental effects on consumer
Unpleasant odour formation
Contamination risk, spread of diseases
Detrimental effects on textiles
Staining and discolouring of textiles
9.9 Effects of microbes on consumers and textiles.
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transfer sites (vectors), offering ideal environments for the proliferation and spread of micro-organisms such as bacteria, fungi and yeasts. In spite of the many precautions taken to prevent the transmission of harmful organisms in hospitals, such as hand-cleaning, housekeeping and laundry protocols, the risk of cross-contamination of surfaces and textiles to patients and staff is considerable. Though the use of antimicrobials has been known for decades, it is only in the last couple of years that several attempts have been made to manufacture antimicrobial textiles, especially by finishing. An antimicrobial finish is a recent innovation in finishes. It prevents the growth of bacteria, and products finished with it have been proved to be environmentally friendly and healthprotecting, preventing diseases. It also prevents garments from acquiring an unpleasant odour.
9.5.2 Antimicrobial treatment on textiles By incorporating an antimicrobial finish into textiles, wearers will be protected from microbiological attack. The antimicrobial agent works either by the slow release of the active ingredient or by surface contact with the microbes. Antimicrobial agents kill micro-organisms or inhibit their growth by interfering with the necessary mechanism of the microbe’s cell, such as by causing:69 ∑ Cell wall damage ∑ Inhibition of cell wall synthesis ∑ Alteration of cell wall permeability ∑ Inhibition of the synthesis of proteins and nucleic acid ∑ Inhibition of enzyme action. However, there are different kinds of antimicrobial finishes, appropriate for different applications and levels of protection. One major application of antimicrobial finish is in the medical field. Medical applications demand powerful bactericidal antimicrobials that will act quickly to help maintain sterile environments. In the case of institutional applications such as uniforms and hotel/restaurant fabric, the antimicrobial would only be required to have a bacteriostatic effect to control stains and odour. Apparel and home textile applications such as active wear, bed linen, hosiery, underwear, carpeting, etc. will also use antimicrobial activity to control odour and staining.
9.5.3 Fabrication of antimicrobial textiles Antimicrobial textiles can be fabricated in two principal ways: ∑
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Antimicrobial treated fibres or fabrics: by post-antimicrobial treatment of the fibre or the fabric during finishing stages.
The efficacy of an antimicrobial finish will depend on various factors, such as its chemical nature, method of application and durability. The selection of the appropriate antimicrobial system used will thus depend on a number of considerations. The first determination is the type of antimicrobial activity desired. The second is the way the system is applied (by padding, exhausting, or incorporating a synthetic fibre containing the antimicrobial agent) and the third is the efficiency and durability of the antimicrobial agent.
9.5.4 Characteristics of an ideal antimicrobial textile ∑
Permanent antimicrobial properties that are not lost during usage or washing. ∑ Antimicrobial activity on a wide range of micro-organisms. ∑ The antimicrobial effect has to be limited on the surface of the textile, so as not to interfere with skin bacteria. ∑ The textile should not contain toxic migrating substances and should comply with the statutory requirements of regulating agencies.
9.5.5 Antimicrobial fibre/yarn The antimicrobial agents can be introduced during fibre formation, or deposited during the finishing processes of yarns or textile fabrics by exhaust, pad–dry–cure, coating, spray and foam techniques. The bioactive substance deposited on the surface of textiles may be easily washed out, and may also disturb the fabric’s usability and comfort. The antimicrobial yarn can be produced by incorporating biologically active substances into the yarns. The textiles manufactured from such antimicrobial yarns permanently contain the bioactive substances in their structure. However, the delivery technologies of antimicrobial yarns may be illustrated as follows (see Fig. 9.10): ∑
Internal antimicrobial release: a viable option for synthetic fibres, where antimicrobials can be incorporated into the fibres when they are spun. ∑ Surface application: applicable to all fibres. The washing durability depends on material affinity. Surface application may interfere with textile handling properties. ∑ Chemical bonding: the best way to achieve durability. It requires suitable reactive groups on the textile. Textile fibres with built-in antimicrobial properties will serve the purpose alone or in blends with other fibres. Bioactive fibre is a modified form of the finish which includes chemotherapeutics in its structure, i.e. synthetic
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= Extrusion
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Polymer Antimicrobial
Physical incorporation of antimicrobial into fibre
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= Coating
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Antimicrobial coated on fibre’s surface
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= Finishing
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Antimicrobial bonded with fibre’s reactive group
(c)
9.10 (a) Physical incorporation of antimicrobial into fibre; (b) surface application of antimicrobial on fibre; (c) chemical bonding of antimicrobial with fibre’s reactive groups.
drugs of bactericidal and fungicidal qualities. These fibres are used not only in medicine and health prophylaxis applications but also for manufacturing textile products in daily use and technical textiles. The field of application of bioactive fibres includes sanitary materials, dressing materials, surgical threads, materials for filtration of gases and liquids, air conditioning and ventilation, constructional materials, and special materials for the food, pharmaceutical, footwear, clothing and automotive industries, etc.
9.5.6 Methods to produce durable antimicrobial fibre/ yarn70 The various methods for improving the durability of the finish include: ∑ Insolubilization of the active substances in/on the fibre ∑ Treating the fibre with resin, condensates or crosslinking agents ∑ Micro-encapsulation of the antimicrobial agents with the fibre matrix
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∑ Coating the fibre/yarn surface instead of the fabric ∑ Chemical modification of the fibre by covalent bond formation ∑ Use of graft polymers, homopolymers and/or copolymerization onto the fibre.
9.5.7 Antimicrobial substances used in yarn or textiles Many antimicrobial agents used in the textile industry are known from the foodstuffs and cosmetics sectors. These substances are incorporated with textile substrates comparatively at lower concentrations. The chemicals used for antimicrobial finishes are organic compounds such as amines or quaternary ammonium compounds, biguanide, alcohols, phenols and aldehydes, mineral compounds such as metal ions, oxides, photocatalysts and organometallic compounds, and natural compounds.71 Amongst the aforementioned agents, complexing metallic compounds based on metals such as cadmium, silver, copper and mercury are very good antimicrobial agents, and silver in its many oxidation states (Ag0, Ag+, Ag2+ and Ag3+) has long been recognized as having an inhibitory effect towards many bacterial strains and micro-organisms. It is also found that nano-silver particles have an extremely large specific surface area, thus increasing their contact with bacteria or fungi and vastly improving their bactericidal and fungicidal effectiveness.72,73 Moreover, nano-silver attacks the problems of unpleasant odour, discoloration and product degradation at their source. The antibacterial properties of nano-silver provide excellent durability at a reasonable cost, and garments made of nano-silver-treated yarns control bacterial growth even after 50 washes. Hence, nano-silver-treated garments, especially intimates and sportswear, carry a promise of lasting cleanliness and freshness. Thus the yarn containing nano-silver antimicrobial agent is called the ‘Body Fresh Yarn’.74 In the field of medicine, hospitals and healthcare facilities have employed the use of silver and its ability to provide antimicrobial coatings to prevent the spread of infection. A recent development in wound closure involves the use of sutures coated with antimicrobial silver substances to reduce the chances of wound infection. These sutures are very effective at inhibiting bacterial growth in wounds. Chitosan is an effective natural antimicrobial agent derived from chitin, a major component in crustacean shells. Coatings of chitosan on conventional fibres appear to be the more realistic prospect since they do not provoke an immunological response. Fibres made from chitosan are also available in the marketplace.75 Regenerated cellulose bamboo fibre has a unique antibacterial and bacteriostatic bio-agent named ‘bamboo kun’. This substance is combined
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with bamboo cellulose during the process of manufacture into bamboo fibre. Bamboo fibre has particular and natural antibacterial, bacteriostatic and deodorization functions. Bamboo fibre’s natural antibacterial function differs greatly from that of chemical antimicrobials. The latter often tend to cause skin allergy when added to apparel.76 Natural herbal products, such as Tulsi (Ocimum sanctum), an Ayurvedic herb, can also be used for antimicrobial finishes since there is a tremendous source of medicinal plants with antimicrobial composition to be effective candidates in bringing out herbal textiles. Herbal textiles will be of great importance because of their healing, soothing and medicinal properties on skin, but the fastness of natural herbal material is poor.77 Plasma treatments are gaining popularity in the textile industry due to their numerous advantages over conventional wet processing techniques. This treatment changes both the physical and functional characteristics of fibres without altering the weight, thickness, breaking strength, elongation, etc. Antimicrobial coating with plasma technology ensures a very durable coating, especially by metal complexes like silver.
9.5.8 Conclusion Growing awareness of health and hygiene has increased the demand for bioactive or antimicrobial yarns. Apart from its industrial use, an antimicrobial finish on yarns has become essential in our day-to-day life to maintain a fresh and hygienic atmosphere. These yarns have excellent potential in various textile uses such as inner wear, household articles and baby care products. Even though many products have already been developed, there is still much scope for textile researchers in this field.
9.6
Yarns for specific purposes
9.6.1 Auxetic yarns78,79 A recent exciting development in textile technology is auxetic fibres that exhibit the unusual property of getting fatter when stretched and narrower when compressed. In fact, these fibres, in contrast to conventional fibres, swell on stretching with consequent increase in their internal void volume. The processing of making auxetic multifilament yarn from polymers such as polytetrafluoroethylene, polypropylene and nylon into knitted and woven textile constructions has been demonstrated by staff at Bolton University, UK.80 One application for auxetic fabrics is in wound bandages that contain a wound-healing agent. As the infected wound swells, so does the auxetic bandage. The internal voids in the bandage expand and release the wound-
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healing agent. Once the wound starts to heal, the swelling goes down, the bandage contracts, and release of the wound-healing agent ceases. Thus, the auxetic fibres provide a means of controlled drug delivery. Auxetic fabrics are also envisaged in compression bandages and arterial prostheses. Auxetic fabrics are particularly desirable in applications that require highly curved hard surfaces, such as those found in the body parts of aircraft and cars. Auxetic textiles are extensively used also for making personal protection clothing, filtration, mechanical lungs, ropes, cords and fishnets, fibrous seals, etc.
9.6.2 Shape-memory yarn78,79,81 Shape-memory materials are those materials that have the ability to ‘memorize’ a macroscopic (permanent) shape, be manipulated and ‘fixed’ to a temporary and dormant shape under specific conditions of temperature and stress, and then later relax to the original, stress-free condition under thermal, electrical or environmental command. Shape-memory materials are widely used in different fields, such as space, biomedical and engineering. Some shapememory materials are used for daily commodities and industrial products. Shape-memory textiles are a wonderful innovation that offers great opportunities for smart products. They are having a significant impact in the textile, clothing and other industries like defence and aerospace. These ‘intelligent’ textiles have the capability of remembering their original shape. No matter what happened to them during their process of change, such as washing or steam treatment, they can still recover their original shape or state under suitable conditions. Shape-memory textile fibre is often divided into shape memory alloy (SMA) fibre/yarn and shape memory polymer (SMP) fibre/yarn. The shape-memory effect of SMA fibre stems from the existence in such materials of two stable crystal structures: a high temperature-favoured ‘austenitic’ phase and a low temperature-favoured (and ‘yieldable’) ‘martensitic’ phase. Deformations of the low temperature phase, occurring above a critical stress, are recovered completely during the solid–solid transformation to the high temperature phase.82 Shape-memory alloy fibres such as nickel–titanium (NiTi) can be incorporated into textiles such as polyester, acrylic, cotton, etc., during textile finishing, fibre and film making. Italy Luotaliyani designed ‘lazy shirt’ fabric combining nickel, titanium and nylon fibre, these shape memory alloy fibres having shape-memory function. In hot weather the wearer can roll up the sleeve from wrist to elbow; when the temperature drops and the sleeve is unrolled it automatically returns to its original shape. The clothing also has super wrinkle-free capacity, regardless of massive pressures, and can return to its original status in 30 s.83
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Despite the demonstrated merits, SMA fibres also show some downsides that limit their application, such as limited recoverable strains of less than 8%, inherently high stiffness, high cost, a comparatively inflexible transition temperature, and demanding processing and training conditions. Polymeric materials are intrinsically capable of a shape-memory effect, although the mechanisms responsible differ dramatically from those of metal alloys. In SMA, pseudo-plastic fixing is possible through the martensitic detwinning mechanism, while recovery is triggered by the martensite–austenite phase transition. Thus, fixing of a temporary shape is accomplished at a single temperature, normally slightly below room temperature, and recovery occurs upon heating beyond the martensitic transformation temperature. In contrast, shape-memory polymers achieve temporary strain fixing and recovery through a variety of physical means, the underlying very large extensibility being derived from the intrinsic elasticity of polymeric networks. Compared with shape-memory alloys, polymeric shape-memory materials possess the advantages of high elastic deformation (strain up to more than 200% for most of the materials), low cost, low density, and potential biocompatibility and biodegradability. They also have a broad range of application temperatures that can be tailored, have tunable stiffness, and are easily processed. These two materials (polymers and metal alloys) also possess distinct applications due to their intrinsic differences in mechanical, viscoelastic and optical properties. Shape-memory yarns are likely to be increasingly significant in future for sutures and stents. For instance, shape-memory implants can be brought into the body in a compressed temporary shape, through a small incision. A suitably constructed implant, on reaching body temperature, would then change to its ‘remembered’ permanent shape. These materials can also be biodegradable, so that repeat surgery for removal of the implant would not be required.
9.6.3 Anti-static yarn Antistatic-yarn is designed to make anti-static textiles to allow the discharge of accumulated static electricity from a person’s skin as well as acting as a barrier against electromagnetic radiation. Anti-static textile is required to prevent damage to electrical components or to prevent fires and explosions when working with flammable liquids and gases. If not controlled, static electricity can cause product damage and lead to machinery downtime, lost man hours, returned products and warranty costs, particularly in the semiconductor and electronics industry. Anti-static properties can be imparted into textiles by either ∑
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enhancing the electro-conductivity of yarns by coating with metal or by conductive polymers such as carbon,84 polypyrrole, polyaniline, etc. (see Chapter 5 for details).
The characteristics of the fabric include an associated earth connection based on textile fibres and conductors and being sufficiently long for the fabric to be electrically connected to the ground, thereby generating a discharge. Such anti-static fabrics are used in cleanroom garments, workwear, carpets, sewing threads, wool garments, brushes, blankets, wrist-straps, anti-static shoes, etc.
9.6.4 Anti-stress yarn Anti-stress properties in yarn can be obtained by imparting various properties into yarns such as electromagnetic shielding property, anti-static property, UV shielding property, antimicrobial property, etc. The anti-stress value can be measured by a Polarity Test Therapy (PTT) machine. It measures the positive (+ or anabolic, contracting) and the negative (– or catabolic, relaxing) energy fields of each material, as well as living (organic) and dead (inorganic) material. The value of the measurements is expressed in degrees between ‘0 to 100 positive, yang, stressed’ or ‘0 to 100 negative, yin, relaxed’. The healthy balance between both is the point zero. Most people in our society today have too much + positive or anabolic energy in their body. This excess of contracting energy, which results in stress, enters the human body through: ∑ Eating too much salt, meat, cheese, etc. ∑ Living environment such as the computer screen, mobile phone, too much car driving, etc. All these cause stress diseases (too much +, too much yang). For example, the anti-static yarn (mentioned above) containing conductive fibres is also an anti-stress yarn as it can shield the human body against electric and electromagnetic waves from electronic devices like cellphones and computers. Electromagnetic waves deplete our natural serotonin and melatonin, the hormones that help guide our sleeping pattern and protect against some pathogenic effects. However, it is recommended for anti-stress yarns to have a relaxing, anti-stressing action between 20 and 30% (negative charge, i.e. de-stressing) and garments made of such yarns give the body a relaxing force of –20 to –30% according to the Polarity Test Therapy (PTT) measurement. In a study, 80% of the people (this means all stressed people) were observed to relieve stress by wearing clothes made of this yarn.85,86
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9.6.5 Anti-allergic yarn Anti-allergic textiles are textiles that are capable of causing a reduction in predisposition to all types of bacterial and fungal allergies such as colds and flu, improvement in sleep, meditation and relaxation, increase of lung capacity, relief from allergies, increased absorption of vitamins B and C, relief from migraine, respiratory tracts and nose disorders, stress, etc. Allergen-blocking products are recommended for allergic subjects; for example, special mattresses and pillow cases are used by patients allergic to dust mites, and pollen masks for hay fever sufferers. Tightly woven cloth physically blocks pollens and the dead bodies/faecal pellets of mites, and decreases allergenic patients’ exposure to these allergens. The major causes of allergies are allergenic proteins released from pollen and mites. Sometimes allergens are decomposed into highly soluble small particles, slip through the cloth by sweat, and come into direct contact with patients. Recently invented phthalocyanine (Pc)-dyed yarn can adsorb allergenic proteins, so it has widespread potential in the manufacture of allergy-alleviating products such as allergen-proof masks or encasements and underwear including socks and hosiery for atopic patients.87 Anti-allergic textiles may also be made from yarns coated with silver.88 A layer of pure silver permanently bonded to the surface of a textile yarn adds an anti-allergic property along with antimicrobial, anti-odour, heat transfer, anti-static and therapeutic properties. Anti-allergic textiles are widely used in the manufacture of beddings, sportswear, hospital uniforms, surgical gowns, masks, etc.
9.6.6 Soluble yarn89,90 Soluble fibres are a newly developed environmental protection fibre. They possess the property of dissolving in water at a particular temperature depending on their composition. Water-soluble PVA fibre has a unique specific property in that it is soluble in hot water below 93°C, and it has high strength, 1.5 to 3 times that of cotton. Water-soluble fibre degrades naturally in soil. Blended yarn can be produced with cotton or other fibres and made into cloth. Since the water-soluble fibre in fabric can be dissolved, the style and grade of the fabric will certainly be greatly improved. After it is processed to water-soluble non-woven fabric it can be used as a disposable cloth such as a computer embroidery cloth, medical clothing, etc. Water-soluble garments are sterile hygienic materials that are used to help protect patients and medical staff from the dangers of the infections to which they are exposed in hospitals. Specific uses include surgical garments and drapes, facemasks and shoe covers. Other than these, different kinds of water-soluble non-woven fabrics
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(40°, 60°, 90°, etc.) are used as backings or bearings on embroidery fabrics, and dissolve totally in hot water after the embroidery is finished. Water-soluble high-strength fibre can be spun into high-strength yarn for the production of high quality and recoverable sacks for cement or fodder, etc. With further development of the water solubility of these fibres, they will be used more and more extensively day by day.
9.7
Future trends
Intelligent textiles, variously known as smart textiles, electronic textiles or e-textiles, have attracted considerable attention worldwide due to their potential to bring revolutionary impacts on human life. Despite much promising progress in this exciting, newly emerged research field, there still exists a continuous effort to develop new textiles to solve different purposes in the coming years. Consumers are demanding textile products with higher performance not only in the areas of ‘traditional’ clothing and home textiles but for technical application also. In fact, significant product differentiation in the area of textiles can be achieved by varying their high performance properties, in parallel with visual appearance. Some of these properties were developed mainly for protective clothing but nowadays they are often present in functional textiles used for normal clothing. Many textile producers are devoting more and more attention to try to put into the market products with new ‘functional properties’ that can represent important added value. Functional properties can be defined as all the effects that are beyond the purely aesthetic and decorative functions. They include a large range of properties that in some cases can also be classified as ‘smart properties’, which means that they grant to the textiles the capacity of acting according to an external stimulation. Multiple functions are often required, leading to what we can call multifunctional textiles. Consumers all over the world are increasingly aware of the importance of a hygienic lifestyle and safety and are demanding and expecting a wide range of textile products meeting enhanced performance requirements. In this context, advancers in technical yarns are in full swing. The performance characteristics of many already existing technical yarns were not even thought of only a few years ago, and it can be said that the novel yarns to meet new demands in the near future have not yet been invented. With the continued advances in new technology and nano-materials, researchers all over the world are being challenged to come up with products for the coming decades that will provide innovative solutions for global problems, such as pollution, health issues, transport, protection, communication, and so on.
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References
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25. Hilfiker R, Kaufmann W, Reinert G and Schmidt E, ‘Improving sun protection factors of fabrics by applying UV-absorbers’, Text. Res. J., 1996, 66, 61–70. 26. Sarkar A K, ‘An evaluation of UV protection imparted by cotton fabrics dyed with natural colorants’, BMC Dermatology, 2004, 4, 15. 27. Yang H, Zhu S and Pan N, ‘Studying the mechanisms of titanium dioxide as ultraviolet-blocking additive for films and fabrics by an improved scheme’, J. Appl. Polym. Sci., 2004, 92, 3201–3210. 28. Madronich S and de Gruijl F R, ‘Skin cancer and UV radiation’, Nature, 1996, 23, 366. 29. Available from: http://www.medterms.com/script/main/art.asp?articlekey=5590 [Accessed 19 March 2009] 30. Gies P, Roy C, Toomey S and Tomlinson D, ‘Ambient solar UVR: personal exposure and protection’, J. Epidemiol., 1999, 9, 115–122. 31. Dummer R and Osterwalder U, ‘UV transmission of summer clothing in Switzerland and Germany’, Dermatology, 2000, 200, 81–82. 32. Hoffmann K, Laperre J, Avermaete A, Altmeyer P and Gambichler T, ‘Defined UV protection by apparel textiles’, Archives of Dermatology, 2001, 137, 1089–1094. 33. Crews P C, Kachman S and Beyer A G, ‘Influences on UVR transmission of undyed woven fabrics’, Textile Chemist and Colorist, 1999, 31, 17–26. 34. Hatch K L, ‘Fry not!’, ASTM Standardization News, 2001, 18–21. 35. Sun protective clothing: evaluation and classification. Sydney, New South Wales: Standards Australia International Ltd, 1996. Australian/New Zealand Standard (AS/ NZS) 4399. 36. Pailthorpe M, ‘Textiles and sun protection: the current situation’, Australas Textiles, 1994, 14, 54–66. 37. Gies H P, Roy C R and McLennan A, ‘UV protection by clothing: an intercomparison of measurements and method’, Health Phys., 1997, 73, 456–464. 38. CEN – The European Committee for Standardization. Textiles: solar UV protective properties: methods of test for apparel fabrics. Stassart, Brussels: CEN, 1999. PrEN 13758. 39. Diffey B L, ‘The CIE ultraviolet action spectrum for erythema’. In: Mathes R and Sliney D, eds, Measurements of Optical Radiation Hazards. Munich, Germany: Märkl-Druck, 1998, 63–67. 40. Bilimis Z, ‘Measuring the UV protection factor (UPF) of fabrics and clothing’, Varian Australia Pty Ltd, Victoria, Australia 3170, 1994, 1–4. 41. Pailthorpe M, ‘Apparel textiles and sun protection: a marketing opportunity or a quality control nightmare?’, Mutat. Res., 1998, 422, 175–183. 42. Davis S, Capjack L, Kerr N and Fedosejevs R, ‘Clothing as protection from ultraviolet radiation: which fabric is most effective?’, Int. J. Dermatol., 1997, 36, 374–379. 43. Mima T and Sato M, ‘Studies on ultraviolet-rays blocking by dyed fabrics: Comparison between direct dye/cellulose and disperse dye/polyester’, AIC 2004 Color and Paints, Interim Meeting of the International Color Association, Proceedings, Available from: http://www.fadu.uba.ar/sitios/sicyt/color/aic2004/171-174.pdf [Accessed 19 March 2009] 44. Robson J and Diffey B L, ‘Textiles and sun protection’, Photodermatol. Photoimmunol. Photomed., 1990, 7, 32–34. 45. Sivaramakrishnan C N, ‘UV protection finishes’. Available from: http://www. fibre2fashion.com/industry-article/1/69/uv-protection-finishes3.asp [Accessed 19 March 2009]
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46. Gabrijel�i� H, Urbas R, Sluga F and Dimitrovski K, ‘Influence of fabric constructional parameters and thread colour on UV radiation protection’, Fibres & Textiles in Eastern Europe, 2009, 17, 46–54. 47. Available from: http://www.sunblock.se/english/sunblock_sunfacts/sunblock_clothing_ sunfacts.htm [Accessed 20 March 2009] 48. Available from: http://www.absoluteastronomy.com/topics/Metallic_fiber [Accessed 25 March 2009] 49. Available from: http://www.fibre2fashion.com/industry-article/3/213/metallic-fibres1. asp [Accessed 25 March 2009] 50. Available from: http://www.directindustry.com/prod/bekaert/metal-fiber-5919-40935. html [Accessed 28 March 2009] 51. John T, ‘Stainless steel yarn fabrics and protective garments’, US Pat. No. 5248548, 28 September 1993. 52. Emery I V, ‘Antistatic textiles containing metallic fibers’, US Pat. No. 3288175, 11 November 1966. 53. Lee S H, ‘Electromagnetic shielding fabric with stainless steel yarn’, Korean Pat. No. 2003061535, 22 September 2003. 54. Fenglian Z, ‘Functional yarns with resistance to radiation and static electricity and electromagnetic wave shielding properties, comprising blends of cotton, polyester, nylon, acrylonitrile or viscose rayon fibers and stainless steel fibers, Chinese Pat. No. 101173393, 7 May 2008. 55. Available from: http://www.wipo.int/pctdb/en/wo.jsp?wo=2000057738 [Accessed 27 March 2009] 56. Available from: http://www.stax.de/englisch/metals.html [Accessed 27 March 2009] 57. Available from: http://www.bikudo.com/product_search/details/72915/sintered_ metal_fiber_felt.html [Accessed 27 March 2009] 58. Chen J M, Chiang S H and Lin J H, ‘Production and application of geogrids with functional stainless steel/polypropylene composite yarns’, Text. Res. J., 2008, 78, 1098–1109. 59. Sydney F, Hanai Jr D and Bento J, ‘Shear behavior of fiber reinforced concrete beams’, Cement & Concrete Composites, 1997, 19, 359–366. 60. Available from: http://www.oike-kogyo.co.jp/english/products/13.html [Accessed 28 March 2009] 61. Available from: http://www.articlealley.com/article_178752_22.html [Accessed 28 March 2009] 62. Available from: http://www.metlon.com/metallic.htm [Accessed 28 March 2009] 63. Lin J H, Lou C W and Liu H H, ‘Process and anti-electrostatic properties of knitted fabric made from hybrid staple/metallic-core spun yarn’, J. Adv. Mater., 2007, 39, 11–16. 64. Chen H C, Lee K C and Lin J H, ‘Electromagnetic and electrostatic shielding properties of co-weaving-knitting fabrics reinforced composites’, Composites Part A: Applied Science and Manufacturing, 2004, 35, 1249–1256. 65. Cheng K B, Ueng T H and Dixon G, ‘Electrostatic discharge properties of stainless steel/polyester woven fabrics’, Text. Res. J., 2001, 71, 732–738. 66. Lin J H and Chiang S H, ‘Manufacturing and mechanical properties of grids braided from stainless steel/pp functional ply yarn’, J. Adv. Mater., Special Edition 1, 2006, 82–86. 67. Available from: http://www.stax.de/englisch/index.html [Accessed 31 March 2009] © Woodhead Publishing Limited, 2010
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68. Dastjerdi R, Mojtahedi M R M and Shoshtari A M, ‘Investigating the effect of various blend ratios of prepared master batch containing Ag/TiO2 nanocomposite on the properties of bioactive continuous filament yarns’, Fibers and Polymers, 2008, 9, 727–734. 69. Intelligent Textile Structures – Application, Production & Testing, International Workshop. Available from: http://texmail.ca/002/files/000MNu00ItFU0mF4XF0x/ Anti-microbial_treatment.pdf [Accessed 24 April 2009] 70. ‘Antimicrobial products in textile industry’. Available from: http://www.fibre2fashion. com/industry-article/11/1017/antimicrobial-products-in-textile-industry1.asp [Accessed 24 April 2009] 71. Bang E S, Lee E S, Kim S I, Kim, Yu Y H and Bae S E, ‘Durable antimicrobial finish of cotton fabrics’, J. Appl. Polym. Sci., 2007, 106, 938–943. 72. Lee H J, Yeo S Y and Jeong S H, ‘Bacteriostasis and skin innoxiousness of nanosilver colloids on textile fibre’, Text. Res. J., 2005, 75, 551–556. 73. Matyjas-Zgondek E, Bacciarelli A, Rybicki E, Szynkowska M I and Kołodziejczyk M, ‘Antibacterial properties of silver-finished textiles’, Fibres & Textiles in Eastern Europe, 2008, 16, 101–107. 74. Mantford C, Fabrics Made From Antimicrobial Microfibres Assist in Controlling Odour. Available from: http://ezinearticles.com/?Fabrics-Made-From-AntimicrobialMicrofibres-Assist-in-Controlling-Odour&id=591957 [Accessed 24 April 2009] 75. Shanmugasundaram O L, ‘Chitosan coated cotton yarn and its effect on antimicrobial activity’, J Tex and Apparel Tech. and Management, 2006, 5, 1–6. 76. Available from: http://www.bamboo-t-shirt.com/BambooYarnsFibers.html [Accessed 24 April 2009] 77. Nagarajan L, Herbal Finishing of Cotton Fabric for Antimicrobial Properties with Ocimum Sanctum. Available from: http://www.fibre2fashion.com/industryarticle/18/1759/herbal-finishing-of-cotton-fabric-for-antimicrobial-properties-withocimum-sanctum1.asp [Accessed 24 April 2009] 78. Mather R R, Developments in Textiles. Available from: http://www.devicelink.com/ mdt/archive/06/10/003.html [Accessed 25 April 2009] 79. Available from: http://www.bch.in/shape-memory-materials.html [Accessed 25 April 2009] 80. Alderson K L, ‘Auxetic polypropylene fibres: Part 1 – Manufacture and characterisation’, Plastics, Rubber and Composites, 2002, 31, 344–349. 81. Meng Q and Hu J, ‘Influence of heat treatment on the properties of shape memory fibers. I. Crystallinity, hydrogen bonding, and shape memory effect’, J App Polym Sci, 2008, 109, 2616–2623. 82. Liu C, Qin H and Mather P T, ‘Review of progress in shape-memory polymers’, J. Mater. Chem., 2007, 17, 1543–1558. 83. Yan L, Aggie C, Hu J-L and Jing L, ‘Shape memory behavior of SMPU knitted fabric’, J Zhejiang Univ Sci, 2007, 8, 830–834. 84. Available from: http://www.kuraray.co.jp/en/release/2007/070208.html [Accessed 25 April 2009] 85. Available from: http://www.viafil.com/ENG/what.htm [Accessed 25 April 2009] 86. Available from: http://www.perunaturtex.com/qoperfin.htm [Accessed 25 April 2009) 87. Yano H, Sugihara Y, Shirai H, Wagatsuma Y, Kusada O, Matsuda T, Kuroda S and Higaki S, ‘Phthalocyanine-dyed fibers adsorb allergenic proteins’, Amino Acids, 2006, 30, 303–305.
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88. Available from: http://www.bch.in/adhesive-material.html [Accessed 25 April 2009] 89. Available from: http://www.bch.in/shape-memory-materials.html#soluble-textiles [Accessed 27 April 2009] 90. Available from: http://www.webspawner.com/users/PVAFiber/ [Accessed 27 April 2009]
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Electro-conductive textile yarns
M. L a t i f i, P. P a y v a n d y and M. Y o u s e f z a d e h - C h i m e h, Amirkabir University of Technology (Tehran Polytechnic), Iran
Abstract: This chapter introduces electro-conductive yarns, which are highly desirable as industrial materials for various applications. It first reviews different methods of manufacture and describes the structure of the electroconductive yarns produced. The instruments for measuring the properties related to conductivity are then introduced. Various potential application areas of conductive yarns in terms of their uses are presented. The chapter also includes two recent academic researches, which have led to the development of novel methods for producing electro-conductive yarns. Key words: electro-conductive yarn, metallic fiber, electro-conductive polymer, carbon nano-tube (CNT) composite fiber, technical textiles.
10.1
Introduction
In the last decade, the use of electrical and electronic devices has rapidly expanded. Similarly, conductive fibers and yarns have drawn considerable attention during recent years. However, metallic yarns have had a long history in prestigious adornment. Since ancient times, humans have exploited metallic material to produce decorative textiles. It can be proven by the study of cultural relics that the production of golden yarns developed in China in the third millennium bc. Nevertheless, in the ancient world, metallic yarns were mostly used to make armor on account of their resistance metals.1 Today’s metallic yarns are used to create fashionable as well as ‘intelligent’ apparel. ‘Intelligent’ and ‘smart’ apparel refers to a class of apparel that has the possibility of an automatic change in properties influenced by external factors (parameters) or sensing them and even taking decisions, which means learning or communication with the environment in addition to traditional properties of clothing, such as healthcare (monitoring, training result diagrams), everyday life (telephone, fitness), sports (training, performance measurement) and leisure (aesthetic customization, network games). Moreover, electrically conductive fibers, yarns and textile structures are highly desirable as industrial materials such as sensors, filters, electrostatic discharge, plastic welds, electromagnetic interference shielding, dust and germ-free clothing, and data transfer in clothing, and also for military applications like camouflage 298 © Woodhead Publishing Limited, 2010
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and stealth.2 Thus, it is important to impart electrical conductivity to yarn in order to modify the general properties of textile structures and to add new functions to them. There are several known methods of manufacturing electro-conductive yarns. The simplest way is to incorporate metal filament into yarns. Another approach is to produce metallic yarns. It is possible to spin regular short staple yarns with metallic fibers. Conductive yarns may be made of a metallic strand core with regular yarns wrapped around it. To improve textile properties such as handle, washability and flexibility, electro-conductive fibers and yarns are produced by wet-spinning or melt-spinning from conductive polymer, or by coating fibers with electro-conductive materials such as metal powder, carbon black, carbon nano-tubes (CNT) or intrinsically conductive polymer.3 The ranges of conductivity can be gained by different methods as well as the textile properties which are important for various applications. The methods for measuring the properties related to conductivity such as electrostatic discharging and wave shielding are introduced in this chapter. In addition, the application of conductive yarns in the automotive industry, protective textiles, fabric design, fashion clothing, sports clothing, household, floor covering, industrial textiles and textiles construction is discussed. Finally, two recent academic researches, which led to the development of novel methods for producing conductive yarns by spinning conductive fibers and direct yarn formation from electro-spun CNT/polymer composite nanofiber, are presented in detail.
10.2
Manufacture and structure of electroconductive yarns
In this section, different methods of producing conductive yarns, such as metal fiber and yarn, composite and nano-composite yarn with conductive filler (CNTs, carbon black, metal powder, etc.), inherently conductive polymers, coating with conductive substance (metal or conductive polymer), twisting metal fibers with conventional yarns, bi-component yarns, plasma treatment, carbon fiber, multifunctional CNT yarns by downsizing an ancient technology, etc., are studied. Moreover, the yarn structure in each method is briefly analyzed.
10.2.1 Conductive yarns containing metallic fibers or filaments When high electrical conduction is needed in yarns, direct use of metallic fibers or filaments in the yarn production process is considered. There are several methods for spinning metallic fibers or filaments with other textile fibers. Some of these methods are introduced in the next sections.
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Production of conductive yarns by friction-spinning Friction-spinning is one of the common methods to make core-spun yarns. Open-end friction core-spun yarns (OFCY) are employed for a number of technical and industrial applications, such as in the automotive industry, aviation, sport, mechanical engineering components, the construction industry, the electronic and electrical industry, etc. Core-spun yarns can be defined as yarns made of a number of components, one or more of which are constrained to be permanently at the central axis, while the remaining components act as a sheath part. Thus, a conductive core-spun yarn can be produced,4 with a sheath of some synthetic and stainless steel staple fibers and a higher permeability stainless steel wire core. In Fig. 10.1 the schematic of conductive yarn spinning by DREF III is illustrated. The advantages of using this system for producing conductive yarn are as follows: ∑
Yarns can be produced with performance or functional fiber components in a central position, without filament breaks and with a desirable strength and complete core coverage. ∑ The method eliminates the necessity for sizing when the yarns produced are used as warps in weaving. The properties of the conductive yarn in this method directly depend on the components used and the feeding direction.
Conductive fibers Compressed air
Drafing unit
Core feed
10.1 Schematic diagram of DREF III friction spinning for producing conductive yarn.4
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Production of conductive yarns by ring-spinning Ring-spinning is the most common and traditional method to produce spun yarns. This is a simple and economical system to make core-spun yarns as well as core-spun conductive yarns.5 A core spinning attachment in ring spinning is shown in Fig. 10.2. The property of the yarn produced depends on metal filament feeding parameters such as: ∑
The angle between the metal filament guide and the front roller (Fig. 10.3) ∑ The position of the metal filament in the front roller (centered or offcentered) ∑ The tension of the metal filament.
Metal filament
Roving
Back roller
Guide device
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Core conductive spun yarn
10.2 Schematic diagram of roving and metal filament core spun yarn spinning mechanism.5 Position 1 Position 2
Position 3
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10.3 Feeding angle of the metal filament.5
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The effect of the position of the metal filament in the front roller is shown in Figs 10.4 and 10.5. If the metal filament is fed to the middle of the front roller, it will be covered by staple fibers in the yarn. If the metal filament is fed from the sides of the front roller, it will be wrapped on the staple fibers in the yarn. Production of conductive yarns by hollow-spinning Hollow-spinning can be used to wrap metal filament on the well draft staple fibers, which is shown in Fig. 10.6.(b),6 or to wind textile filaments around
Conductive filament
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Hollow spindle with filaments package Tangential belt Take-off rolls (a)
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10.6 Schematic diagram of hollow spindle spinning system:7 (a) winding textile filaments around metal filament;6 (b) wrapping metal filament on drafted staple fibers.
2 1
1: Conductive filament 2: Textile filament
10.7 Structure of uncommingled conductive yarn.6
the metal filament (Fig. 10.6(a)), which is more desired.7 The method is used to make uncommingled metal yarns which are applied to electromagnetic shielding. The structure of the conductive yarn produced by this method is shown in Fig. 10.7. The uncommingled yarn consists of three different components: the core yarn, the effect yarn and the binding yarn. The matrix PP fibers are used as binding and effect yarns. The reinforcement glass fibers and/or conductive filler copper wires are used as the core yarn (see Fig. 10.7). The property of this type of yarn depends on constituent material combinations and also spinning conditions such as twist, draft and winding.
10.2.2 Inherently conductive polymer (ICP) Conductive polymers are still a developing area. Some inherently conductive polymers are polyaniline, polyvinyl alcohol, polypyrrole and polyamide 11. Amongst these polymers polyaniline has attracted a lot of attention due to its good environmental, thermal and chemical stability. Although it
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was discovered over 150 years ago, only recently has polyaniline captured the attention of the scientific community due to the disclosure of its high electrical conductivity.8 There are many papers concerning the use of polyaniline itself or blended with other polymers.9 For example in the melt spinning process, polyaniline, polypyrrole and graphite are used in order to obtain conductive polypropylenebased fibers with specific electrical and mechanical properties. Polyaniline is treated using dodecylbenzene sulfonic acid (DBSA) to improve the solubility and the dispersion of polyaniline in xylene.10 Conductive polymers like polyaniline are gaining more and more importance due to their advantages, but these polymers are still rather costly and hazardous. They can be used in applications where flexibility, low weight and conductivity are required.
10.2.3 Bicomponent yarns A polymer filled with solid conductive materials forms a stripe (or stripes), a sheath, a core, an offset core, or some combination within the thread line. The second polymer (the carrier or unfilled polymer) provides strength, elongation, and tensile properties. Hancock and Baker11 explained how multi-component electrically conductive fibers can be produced by co-extruding. The fibers contain two polyester components which have a 10°C melt temperature difference between the first and second polyesters and electro-conductive materials are dispersed in one of them.
10.2.4 Conductive CNT yarns Due to the exceptional properties of carbon nano-tubes (CNTs) such as their unique one-dimensional structure, very high aspect ratio and excellent mechanical, thermal and electrical behaviors,12,13 they have secured a place for themselves in several diverse and highly crucial application areas such as nano-electronic devices, nano-scale structural materials, biological probes, next-generation actuators and sensors, functional fabric and e-textiles, fuel cell electrodes, supercapacitors and field emission devices. In the textile field, researchers are using CNTs in different methods for producing fiber and yarn. Electro-spun fiber A powerful method for producing polymer composites is electro-spinning, which utilizes an applied electric stress to draw out a thin nanometerdimension fiber from the tip of a sharp conical meniscus. The focusing of the flow due to converging streamlines at the cone vertex ensures alignment
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of the CNTs along the fiber axis, thus enabling the anisotropic property of CNTs to be exploited. Electro-spinning is employed to develop novel CNT-based piezoelectric strain sensors. The resulting sensors are characterized by performing structural vibration experiments to evaluate their strain-sensing performance. When these new CNT-based piezo-polymer composites are electro-spun and employed into smart fabrics, the strain-sensing ability (as measured by the voltage across the sensor) is increased by a dramatic 35 times, from 2.4 to 84.5 mV for 0.05 wt% of CNTs. The dominant mechanism responsible for such improvement is found to be the alignment of dipoles in the piezoelectric material. Such alignment is mainly due to the ability of the electro-spinning process to generate very thin fibers from polymer-CNT solution. The direct and reverse conversion of electrical energy into mechanical energy in the proposed sensors can create a platform for developing next-generation smart fabrics with applications in membrane structures, distributed shape modulation and energy harvesting.14 Electrophoretic spun fiber Gommans et al. have electrophoretically spun carbon fiber from purified laser vaporization grown single wall nano-tubes (SWNTs) dispersed in N,N-dimethylformamide (DMF) at a concentration of about 0.01 mg/ml. The carbon fiber is turned into a positive electrode by applying voltage, causing the SWNTs to migrate toward it and to form a cloud around the carbon fiber. SWNTs migrate because they are negatively charged in DMF and move electrophoretically toward the positively charged carbon fiber. As the carbon fiber is slowly withdrawn from the suspension, another fiber, attached to its end, is spontaneously formed from the SWNT cloud. The fiber length is limited by the travel distance of the translation stage, the size of the SWNT cloud, and the smoothness of the withdrawal from the solution. Fibers are typically several centimeters long with diameters between 2 and 10 mm. The mass of SWNTs below the bath surface and the surface tension in the meniscus promote the coalescence and axial alignment of bundles of SWNTs.15 Recondensed fiber Vigolo and co-researchers used a recondensing method for producing CNT fibers.16 The process consists of dispersing the SWNTs in surfactant solutions, recondensing the CNTs in the flow of a polymer solution to form a CNT mesh, and then collating this mesh to a CNT fiber. Flow-induced alignment may lead to a preferential orientation of the CNTs in the mesh that has the form of a ribbon (Fig. 10.8).
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Pumping out PVA solution
Injection of SWNTs Dispersion
PVA solution
SWNTs ribbon
Rotating stage
10.8 Schematic diagram of the experimental set-up used to make nano-tube ribbons.16
Flow-induced alignment of the CNTs takes place at the tip of the capillary. The ribbons can be drawn in their third dimension and form a helical structure when the polymer solution is slowly pumped out from the bottom of the container. The injection rate of the SWNT dispersion is varied from 10 to 100 ml/hour. The polymer solution is in a cylindrical container that rotates at speeds ranging from 30 to 150 rpm. The capillary tip from which the CNT solution is extruded is located at about 3.5 cm from the rotation axis of the polymer solution.16 Solution spun fiber Most SWNT fibers have been produced by the solution spinning process. Solution spinning is more complicated than melt spinning because the solidification of fibers involves additional steps. The fiber-forming material is dissolved or finely dispersed into a solvent, and the solvent is extracted after the extrusion to form solid fibers. Therefore, solution spinning is typically used to produce fibers from materials that are decomposed before reaching their melting point or do not have a suitable viscosity for stable fiber formation. Solution spinning is particularly effective for spinning fibers from stiff polymer molecules. Several research groups have used solution spinning to produce bulk quantities of SWNT fibers (continuous lengths of 1 m or more). Solution spinning can be considered as a four-step process:
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Dispersion or dissolution of fiber materials into a solvent Mixing and spinning the solution Coagulation and drawing it into a solid fiber Post-processing of the fiber through subsequent washing, drying, or annealing steps.
Solution spinning can be divided into two main categories: dry and wet solution spinning (Fig. 10.9). The first step of the solution spinning process, dispersal into a solvent, is far from trivial for SWNTs17 due to their high van der Waals interactions.
CNT-PVA conductive filament
Take-up roller
Coagulation bath
10.9 Schematic drawing of a table-top wet-spinning apparatus.18
Melt spun fiber Melt spinning is used to produce many polymer fibers, such as nylon and polyethylene terephthalate fibers. It can be applied to single-component as well as composite fibers. In melt spinning, the fiber-forming material is melted and extruded under tension typically into cooled air. The rapid cooling induces the solidification of fibers. Some polymer/SWNT composite fibers where polymer is the major constituent are produced using this method. However, SWNTs decompose without melting at approximately 750°C in air and at approximately 2000°C in an inert atmosphere (e.g., argon). Thus, melt spinning is not a viable option for fibers where SWNTs are the sole component.19 Haggenmueller et al. produced SWNT polymethylmethacrylate (PMMA) films and fibers.20 Increasing SWNT content dramatically increases the melt viscosity; this results in a melt fracture evidenced by surface roughness, striations along the fiber axis, and non-uniform diameter. Increasing the SWNT weight fraction also decreased the attainable draw ratios and increased the frequency of fiber breaks. Fibers are successfully produced from loadings up to 8 wt% SWNT. The 10 wt% SWNT mixture is too viscous to be extruded. Mechanical and electrical properties depend on SWNT concentration and draw ratio. For melt-pressed films, at a draw ratio of l = 4, the electrical resistance in the direction parallel to processing is decreased from 8.5 Wm at 1.3 wt% SWNT to 0.087 Wm at 6.6 wt%. In the direction perpendicular to processing, the electrical resistances are slightly higher (12.8 Wm and 0.14 Wm, respectively).
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Direct yarn spinning Some reports and papers introduce new methods for spinning CNTs directly from their array.21 Researchers at UT-Dallas University and CSIRO are able to take CNTs directly from the substrate, spin them into yarn and twist that yarn onto a bobbin22–24 (Fig. 10.10). These yarns deform over large strain ranges, reversibly providing up to 48% energy damping, and are nearly as tough as fibers used for bulletproof vests. Unlike ordinary fibers and yarns, these CNT yarns are not degraded in strength by overhand knotting. They also retain their strength and flexibility after heating in air at 450ºC for an hour or when they are immersed in liquid nitrogen. High creep resistance and high electrical conductivity are observed and retained after polymer infiltration, which substantially increases the yarn strength. Li et al. spun fibers and ribbons of CNTs directly from the chemical vapor deposition (CVD) synthesis zone of a furnace using a liquid source of carbon and an iron nano-catalyst.25 Zhang et al. spun continuous yarn from super-aligned carbon nanotube arrays26 (Fig. 10.11). Li et al. claimed that compared to previous works, their approach to grow long (4.7 mm) CNT arrays is simple, safe and cost-effective. Moreover, their CNT arrays are spinnable in a wide range of lengths (0.5 to 1.5 mm) and are much longer than those reported previously. Such long arrays have resulted in CNT fibers with superior strength and electrical conductivity.27 Coating processes In one research, the coating process was carried out on five common fibers, including natural fibers and synthetic fibers, by using a blend of CNTs and PVA. The conductive yarns were treated by an acetylization process in order to decrease the solubility of PVA to water. PVA is one of the best choices 100 mm
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Tensile stress (MPa)
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700 600 500 400 300 200 100 0 0
Yarn-2 Yarn-4
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10.10 (a) SEM images of a CNT yarn in the process of being simultaneously drawn and twisted; (b) stress–strain curve for two single spun CNT yarns22 (reprinted with permission from Elsevier).
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0.4 0.3 0.2 0.1 0.0 0.0
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10.11 (a) Spinning continuous yarns from super-aligned CNT arrays; (b) stress–strain curves of ethanol-treated and further heat-treated CNT yarns.26 (copyright Wiley-VCH Verlag GmbH & Co. KGaA, reproduced with permission).
for use in the coating process on common fibers, including both natural and artificial fibers, because more functional groups in the chemical structure exist for PVA, which could interact with the substrate fibers. The linear resistance of PVA/CNT coated yarn can be reduced to 250 W/cm.18 Shim et al. demonstrate a simple process of transforming general cotton threads into intelligent e-textiles using a polyelectrolyte-based coating with CNTs. The efficient charge transport through the network of CNTs is 20 W/cm. Along with integrated humidity sensing, they demonstrate that CNT-cotton threads can be used to detect albumin, the key protein of blood, with high sensitivity and selectivity.28 Using a dye-printing approach, the CNTs are directly applied to polyester multifilament yarns to form an electrically conductive layer over them (Fig. 10.12). In this method, yarns with electrical resistivity ranging from 103 to 109 W/cm are obtained. Yarns with a resistivity of 103 W/cm can be used to form flat, soft, portable electrical heaters by vertically weaving them into fabrics. The 105 W/cm yarns are employed in anti-static clothing, and the 109 W/cm yarns are used as brushes in photocopying machines.29
10.3
Measurements
In this section, the instruments for measuring the properties related to conductivity are introduced.
10.3.1 Electromagnetic shielding effectiveness measurement (EMSE) In recent years, conductive yarns have been considered for electromagnetic shielding purposes in various applications for the defense, electrical, © Woodhead Publishing Limited, 2010
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Dyeing bath (40°C) Oven (170°C)
Vibration (200 Hz)
10.12 Schematic diagram of dye-printing system for mass production of CNT-dyed multifilament yarns.29
and electronic industries. This is mainly due to their desirable properties in terms of flexibility, electrostatic discharge, EMI protection, radio frequency interference protection, thermal expansion matching, and light weight.30 In order to test and evaluate the electromagnetic shielding effectiveness of conductive yarns, they should be altered to fabric form and the ASTM 4935 or ASTM ES7 standard test method can be used for EMSE measurement, as described below. Shielding effectiveness measurement (ASTM 4935)31 A coaxial transmission line method specified in ASTM D4935-99 is used to test the EMSE of conductive textile composites. The specimen is prepared with the standard test size as shown in Fig. 10.13. The diameter of the outer ring of the specimen is 133 mm. Two specimens are required to be prepared for test, one for reference and another for load testing. Many researchers have described the set-up and testing procedure using a planewave electromagnetic field in the frequency range of 30 MHz to 1.5 GHz. The spectrum analyzer and shielding effectiveness test fixture are used to measure the EMSE (Fig. 10.14).
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30°
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10.13 Specimen dimension for reference (left) and load test (right) ASTM D4935 (unit: mm).32
10.14 Set-up of EMSE testing apparatus according to ASTM 4935.33
Shielding effectiveness measurement (ASTM ES7)31 A coaxial transmission line method specified in ASTM ES7-84 is used to test the EMSE of the conductive textile composites. The specimen is prepared with the standard test size as shown in Fig. 10.15. The calibration specimen for the coaxial tube should be flat and washer-shaped with an outer diameter of 99.75 mm and an inner diameter of 43.70 mm. Its thickness is approximately
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Ø99.75
Ø43.70
10.15 Specimen dimension for ASTM ES7 (unit: mm).31
3 mm. It should be covered on one side with a gold film having a resistance of 5 ± 2W. Figure 10.16(a) indicates a pair of Teflon rings used as a sample holder, Fig. 10.16(b) a specimen for test, and Fig. 10.16(c) a calibration ring. The pair of Teflon rings with low dielectric property is to hold the flexible textile fabric to assure good contact to the specimen holder and a continuously conducting surface around the periphery of the specimen. The inner and outer edges should be coated with a commercial silver paint. The transmission test specimens should be flat and washer-shaped, machined from the material to be measured for shielding effectiveness identical to the calibration specimen. The ASTM ES7-83 has described the set-up and testing procedure using a plane-wave electromagnetic field in the frequency range of 30–1000 MHz. The network analyzer and a coaxial transmissionline cell are used to measure the EMSE.
10.3.2 Electrostatic discharge measurement (ESD)32 The purpose of the electrostatic discharge (ESD) immunity test is to organize a common and reproducible basis for evaluating the performance of electronic and electrical equipment, system, subsystem and peripherals when subjected to ESD. Additionally, this test includes ESD that may originate from personnel and affect objects near essential equipment. They may be involved in static electricity discharges owing to environmental and installation conditions, such © Woodhead Publishing Limited, 2010
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(a)
(b)
(c)
10.16 (a) Specimen holders made of Teflon; (b) specimen of conductive fabric; (c) calibration specimen.31
as low relative humidity, use of low-conductivity carpets, curtains, artificial garments, etc. A transfer of electrical charge between bodies of different electrostatic potential in proximity or through direct contact may result in electrostatic discharge. Thus, the immunity is the ability of a device, equipment or system to perform its function without degradation in the presence of an electromagnetic interference. A 12 kV discharge test is performed using a contact method. The discharged electrode of the ESD generator is held in contact with the test sample, and the discharge is actuated by a spark to the target plane (Fig. 10.17).
10.4
Applications
This section presents various potential application areas of conductive yarn by considering their uses.
10.4.1 Wireless communication Wireless communication with environments requires antennas. Many researches have been done to use conductive yarns as antennas in clothing, especially in military, fire service, high-risk groups, etc.33–36
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Generator
Rd Cs
Rc = 50–100 mW Rd = 330 W Cs = 150 pF 15 kV
Discharge switch
Face of EUT
Discharge return connection Sharp point
(a)
(b) 40° 25°
10.17 (a) ESD generator and (b) discharge tip for contact method.32
10.4.2 Electrical energy and data transportation Because of their high conductivity, metallic conductive yarns are properly used for transportation between electrical sources and electronic devices, which can be sensors, light, etc., or to transport the received information from these devices to the processing part in cloth.37 However, to achieve better textile properties, many studies have been carried out on the use of polymeric-based conductive yarn such as CNT, carbon black or metal powder instead of metallic yarns. Some applications of conductive yarns as electrical energy and data transportation are in wearable electronics, healthcare, textronic and protective textiles.
10.4.3 Textile electrodes and sensors Considering that clothes have a direct connection with the human body, an important function of textronic clothes is to look after human safety. The best way to achieve this is to detect hazards and counteract them effectively. Moreover, clothing must satisfy the individual’s preferences concerning his or her physique, trends in fashion, affordability, aesthetic taste, etc. For this purpose, sensors and actuators should have a fiber shape and electrically conductive features.38 Over the past decade many studies have been carried out to produce conductive yarns as textile electrodes. Researches are now concentrated on the effect on the textile electrodes of factors such as textile pore size and density, textile production and composition, the thickness and structure of the skin, and the condition of the human body. The sideeffects of different kinds of textile electrodes on the human body such as allergic reactions, irritation, toxicity, etc. have also been researched in recent years.39
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10.4.4 Electromagnetic shielding Electromagnetic shielding effectiveness (EMSE) is defined as the degree of shielding against electromagnetic interference at a specific frequency. Electromagnetic energy is absorbed, reflected or transmitted by materials. An important factor for all electromagnetic shielding textiles is to contain a suitable amount of conductive yarns or other conductive components since they weaken the electromagnetic weaves by reflection.40 Therefore, the materials intended to be utilized in electromagnetic shielding applications should be electro-conductive. Smoother surfaces are preferred for better shielding effectiveness. It is known that the best materials used for electromagnetic shielding are based on metals. Metals are known to reduce the effects of radio waves, electromagnetic and electrostatic fields.41 The effectiveness of these materials depends on the type of material used, connections of the conductive net and the frequency of the electromagnetic wave. However, since metal-based materials have some disadvantages such as rigidity, heavy weight and weak comfort properties in end-use, they are increasingly being replaced by conductive polymers, especially for commercial applications, due to their high flexibility, light weight, low cost, etc.
10.4.5 Anti-electrostatic Electrostatic discharge (ESD) phenomena are known to damage sensitive microelectronic devices and systems in the electronics industry and to cause a risk of explosion in flammable atmospheres, e.g. in the chemical industry.42 Although charging and discharging often occur during industrial processes or in automated assembly lines, personnel are still a significant source of harmful discharges. Thus, textiles used in personal protective clothing play an important role in the control of static electricity.43 Materials used to control ESD should not be easily charged and, if charges are generated, they should be safely dissipated. Therefore, conductive yarns are best to use in these cases. One of the earliest applications of conductive yarns was as an anti-electrostatic material, especially in automotive and home textiles like carpets, blankets, covers, etc.44
10.4.6 Anti-bacterial45 Using conductive yarn in anti-bacterial textiles has long been established. Fibers coated by silver particles have been in medical use for antimicrobial and anti-fungal functionality in bandages, dressings and medical devices since the 1990s. Both silver-coated fiber and carbon fiber fabrics are also used to absorb odors. In some recent studies, the effect of an electric-pulsed field in conductive yarns on microbial inactivation is considered.
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10.4.7 Thermal purposes Electro-thermal elements have been incorporated into fabrics for many years. The limitation, so far, has been the low capacity of portable batteries, and the durability of the wiring system.46 The rapid development of conductive yarns with textile properties like flexibility and washability has overcome the durability problem of the wiring system.47,48 However, there seems to be a long way to go to reach a light, small, high capacity and flexible portable power source that would be suitable to use for wearable purposes.
10.5
Future trends
In this section, two recent academic researches that have led to the development of novel methods for producing conductive yarns by spinning metallic fibers and direct yarn formation from electro-spun CNT/PAN composite nano-fiber are described in detail.
10.5.1 Rotational magnetic field aided interlacing of metallic filaments49 The main aim of this work (reproduced here by kind permission of Springer Science + Business Media) is to insert rotational movement to conductive filaments by a mechanism which can operate without any twister. Thus, filaments are not abraded in the twist zone and their rotational movements are not provided by a mechanical driver. By considering the electrical conductivity of filaments and the effect of a rotational magnetic field on a wire with electric current, it seems that the principle of rotational magnetic force on current-carrying wires can be employed to interlace conductive filaments. Laboratory set-up and experimental results The displacement of metallic filaments is the amount by which they are bent when exposed to the forces mentioned above. The laboratory set-up is shown in Fig. 10.18. Suitable DC motors are used to drive the feed-rollers and take-up rollers and to rotate the pulley of magnets. Thus, the speeds of these parts can be controlled to investigate their effects on the interlacing of filaments. The interlacing box contains two strong Nd–Fe–B permanent magnets (PMs) whose properties are shown in Table 10.1. From the table, the magnetic field of each magnet is about 1.14 tesla which is enough for the experimental work. The magnets are placed in two adjustable aluminum boxes to enable variation of the distance between the PMs and, hence, to change the flux density of the operating point. To force most of the magnetic
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Creel
Interlacing zone Magnet covers
Production roller
10.18 The laboratory set-up. Table 10.1 Properties of Nd–Fe–B magnets (sintered) Code
N-33
Residual flux density, Br Coercive force, Hc Intrinsic coercive force, iHc Maximum energy product, (BH)max Curie temperature, TC Maximum operating temperature, TW Dimensions:
≥ 1.14 tesla ≥ 840 kA/m ≥ 960 kA/m ≥ 248 kJ/m3 310°C 80°C 4 ¥ 5 ¥ 2 cm3
flux to go through the air-space containing the filaments, the frame of the interlacing box and all parts which are close to the magnets are made from non-ferromagnetic materials. Two conductive filaments are fed to the interlacing box to test the operation of the designed system. The properties of the conductive filaments are shown in Table 10.2. After many preliminary tests, the setting of the set-up is adjusted so that it reaches a stable condition and an acceptable result. The air-space and the speed of PMs are fixed to 5 mm and 500 rpm, respectively. The currents in the filaments are set equal to 2 amperes. The speed of feeder and product rollers are set to 12 rpm and 10 rpm respectively to have a proper overfeed for false twisting. Figure 10.19 demonstrates the two filaments interlaced by the prototype system, while the influence of rotational speed on the number of interlacing points is illustrated in Fig. 10.20. Experiments show that to © Woodhead Publishing Limited, 2010
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Copper
Conductivity Relative permeability Diameter Density Shearing load Tensile strength Modules Cross-section
56,000,000 S/m 1 70 mm 8.96 g/cm3 95 cN 0.24 GP 5.32 N/tex Circular
1 mm
1 mm
10.19 Two conductive filaments interlaced by the proposed method.
1.2 Interlaces/cm
318
1 0.8 0.6 0.4 0.2 0
100
150
200
250
300 rpm
350
400
450
500
10.20 Effect of rotational speed of the magnetic field on the number of interlaces per centimeter.
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allow filaments to be interlaced, at least 10% overfeeding in the interlacing zone is required. The number of interlacing points directly depends on the rotation speed of the magnetic field. The mechanical and electrical analysis of the proposed method demonstrates the feasibility of metallic (conductive) filaments being interlaced by rotational magnetic field. The interlaced filaments produced by the invented interlacing box prove the proficiency of the method.
10.5.2 Rotational electromagnetic field aided false twisting of metallic filaments50 In the previous study, the theoretical and experimental analyses demonstrated the feasibility of the twister-less method, which interlaced current-carrying metallic filaments applying the rotational magnetic field provided by permanent magnets. The proposed method faced the limitation of the magnets’ rotational speed because of their mechanical driver. To overcome this limitation, the effect of an electromagnetic field on metallic filaments with electrical current is being studied (reproduced here by kind permission of Taylor & Francis LLC). The principle of the single-phase run-capacitor induction motor is used for this purpose. Small power (generally below 2 kW) induction machines have to operate mostly with single-phase AC power supplies that are readily available. For constant-speed applications (the most frequent situation), the induction motor is fed directly from the available single-phase AC power grids. In this sense, it is called the single-phase induction motor. To be self-starting, the induction machine needs a traveling field at zero speed. This, in turn, implies the presence of two windings in the stator, while the rotor has a standard squirrel cage. The first winding is called the main winding, while as shown in Fig. 10.21 the second winding is called the auxiliary winding. As observed, the rotational rotor is the cause of phase differences in the stator poles, which make the rotational magnetic field. It seems that by replacing the rotor with metallic filaments, they can be twisted with each other as illustrated in Fig. 10.22. Since the space between the stator poles is too big to induce current in the filaments, a DC current is used in the filaments. The metallic filaments, as shown in Fig. 10.22, which are carrying opposite currents, are fed to the center of the rotational electromagnetic field provided by a single-phase run-capacitor induction stator. The forces induced in the filaments are: ∑ ∑
Electromagnetic force between two current-carrying filaments Electromagnetic force between current-carrying filaments and the rotational electromagnetic field
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(c)
(a)
(b)
10.21 Schematic diagram of run capacitor single-phase induction motor: (a) main winding; (b) auxiliary winding; (c) rotational rotor.
(a)
(b) dc current
(c)
10.22 Schematic diagram of false twisting zone: (a, b) metallic filaments; (c) run capacitor single phase induction stator.
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∑
321
Electromagnetic force exerted by the interaction of the induced current from the back electromotive force to a filament by a rotating electromagnetic field.
Laboratory set-up and experimental results A suitable single-phase run-capacitor induction motor is used to make a rotational electromagnetic field. The motor properties are provided in Table 10.3. Figure 10.23 shows the laboratory set-up in which the filaments are statically fed to the rotational electromagnetic zone. The filament ends are connected together and fixed. The lengths of the filaments are equal to the stator height and their current can be adjusted up to 3 A. For simplicity and comparing experimental work with theory, two filaments are used in the rotational electromagnetic field. The motor voltage is kept below 110 V to avoid generating heat in the stator winding. For continuous work, it is necessary to design a cooling system for the stator frame. Current circulation in the filaments and the stator simultaneously leads to interlacing filaments for less than one second. Increasing the testing time does not form additional twists. This is because, by growing interlacing points, the filaments make a short circuit which gradually comes out of the induction stator. In this way, the main force (in Table 10.4) is omitted. Figure 10.24 shows the results. As can be observed, the false twisted filaments contain two twisted parts with different directions and a non-twisted part in the middle. The size of the non-twisted part is varied in experiments. The formations in the twisted parts are illustrated in Fig. 10.25. Results show that the twist shape depends on the initial position of each filament in the inner stator space. A filament that is near the inner stator frame experiences more rotational forces. The forces on each filament can be theoretically calculated by applying the parameters of the laboratory set-up (Table 10.4). It can be observed Table 10.3 Single-phase run-capacitor induction motor properties Voltage Power Frequency, w Main winding resistance, Rm Auxiliary winding resistance, Ra Main winding turns, Nm Auxiliary winding turns, Na Main winding current, Im Auxiliary winding current, Ia Capacitor Inner stator diameter Rotor diameter
220 V 240 W 50 Hz 62 ohm 62 ohm 900 900 0.6 A (at 110 v) 0.3 A (at 110 v) 270 VAC, 6 MFD 20 mm 19 mm
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(b)
(a)
(d)
(c)
10.23 Laboratory set-up: (a) single-phase run-capacitor induction stator; (b) feeding part; (c) single-phase run-capacitor induction driver; (d) filament current controller.
from Table 10.4 that the dominant force is the one induced between a current-carrying filament and the rotational electromagnetic field, while the effect of the magnetic force between two current-carrying filaments can be almost ignored. Comparing the magnetic forces in the present work and in the previous study, one can conclude that the magnetic force caused by the current from the induced electromotive force and the rotational electromagnetic field on the filaments are significantly increased. We can perceive that the supplied frequency directly affects this force. The number of interlacing points in proportion to the filament’s current at constant frequency (50 Hz) is illustrated in Fig. 10.26. The effect of frequency on filaments is also considered. Experiment shows
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Table 10.4 Magnetic forces induced on each filament in the twisting box (constants: Ia = 0.3 A, Im = 0.6 A, w = 50 Hz) Force The electromagnetic force between two current-carrying filaments The electromagnetic force between a current-carrying filament and the rotational electromagnetic field The electromagnetic force caused by the current from induced electromotive force and the rotational electromagnetic field on the filament
N/Cm 9E – 7 to 1.8E – 4 (depending on filament position) Approximately 0.1 cos q Approximately 0.05 cos2 q
1 mm
1 mm
1 mm
10.24 Current-carrying metallic filaments false twisted by rotational electromagnetic field.
that (Fig. 10.27) by increasing the frequency the number of twists increases rapidly; around 80 Hz the twist number falls down and filaments higher than 120 Hz cannot be twisted. However, the twist should be theoretically increased by increasing the frequency. Further investigation shows that common electrical motors like the one used in this research are designed to work at 50 Hz; therefore, for higher frequencies a special stator made of ferrite material should be designed. The electrical analysis of the developed method demonstrated its feasibility to interlace metallic filaments in the form of false twist by rotational electromagnetic fields. The interlaced filaments produced by the invented twisting box prove the capability of the applied technique.
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1 mm
1 mm
1 mm (a)
(b)
(c)
(d)
10.25 Twist formation in filaments: (a, b) filaments with same initial position in magnetic field; (c, d) filaments with different initial position in magnetic field. 16 14
Turns/cm
12 10 8 6 4 2 0 0.5
1
1.5 2 Filament current (A)
2.5
3
10.26 Filament current versus number of interlacing points. 120 Twist increase (%) (compare to 50 Hz)
1 mm
100 80 60 40 20 0 60
70
80 90 Magnetic field frequency
100
110
10.27 Effect of electromagnetic field frequency on filament twisting.
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2.000E+01
Z
–2.00E+01
Z (cm)
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Y –5.00E–02
–2.000E+01 –2.000E+01
Y (cm)
X
2.00E+01
Plot type: Contour Plotted quantity: Phi Min contour: 0.0000E+00 Max contour: 1.6000E+04 Contour int: 5.3333E+02 0.0000E+00 1.0667E+03 2.1333E+03 3.2000E+03 4.2667E+03 5.3333E+03 6.4000E+03 7.4667E+03 8.5333E+03 9.6000E+03 1.0667E+04 1.1733E+04 1.2800E+04 1.3867E+04 2.000E+01 1.4933E+04
Plate I Simulation of five simultaneous positive needles in the electrospinning set-up.
2 Colour plate
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10.5.3 Direct conductive electro-spun CNT composite yarn formation A novel technique for producing continuous conductive yarn from composite nano-fibers using an electro-spinning process is introduced in this section. Due to the special properties of CNTs such as their unique one-dimensional structure, low weight, excellent mechanical behavior, and thermal and electrical properties, electro-conductive nano-fibers can be produced from CNT composites. In this technique, CNTs that are well dispersed in the polymer solution are fed to multi-syringes. By applying a high voltage between the syringe needles and a collector, multi-nano-fibers are formed. CNTs in the nanofiber structure become more aligned because of the high electrical force applied to the tip of the needles.51 Using an auxiliary positive disk or ring and collecting nano-fibers from the surface of the water, it is possible to take off multi-nano-fiber yarns directly after electro-spinning without any breakage and with a smooth surface. For increasing the interconnections between nano-fibers, they are immediately twisted after collecting using a dynamic water vortex.52 A high degree of orientation for the CNTs in the nano-fibers is identified via TEM and the orientation of the nano-fibers in the yarn is observed by SEM images. Figure 10.28 shows a SEM image of an electro-spun yarn sample.
10.28 SEM image of nano-fiber yarn produced by the method presented.
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The position and the amount of applied voltage into the needles (electrodes) are very important for the design of the set-up. Thus, the electrical field is simulated and its profile and intensity are investigated to achieve the optimum configuration. In Plate I (between pages 324 and 325), the simulation for five needles is shown. The proposed electro-conductive yarn formation method is expected to become an enabling technology for a variety of textile-related applications such as energy harvesting, vibration dampening, pressure sensors, circuit designs and other special usages.
10.6
References
[1] Jiang S Q, ‘The use of metallic effects in the innovative design of textile fabrics’, PhD thesis, Hong Kong Polytechnic University, 2005. [2] Kim B, Koncar V, Devaux E, Dufour C and Viallier P, ‘Electrical and morphological properties of PP and PET conductive polymer fibers’, Synthetic Metals, 2004, 146, 167–174. [3] Xue P, Park K H, Tao X M, Chen W and Cheng X Y, ‘Electrically conductive yarns based on PVA/carbon nanotubes’, Composite Structures, 2007, 78, 271–277. [4] Ueng T H and Cheng K B, ‘Friction core-spun yarns for electrical properties of woven fabrics’, Composites, 2001, A 32, 1491–1496. [5] Lou C H, ‘Process of complex core spun yarn containing a metal wire’, Textile Research Journal, 2005, 75, 6, 466–473. [6] Cheng K B, Ramakrishna S and Lee K S, ‘Electromagnetic shielding effectiveness of copper/glass fiber knitted fabric reinforced polypropylene composites’, Composites, 2000, A 31, 1039–1045. [7] Lin H J and Lou C W, ‘Electrical properties of laminates made from a new fabric with PP/stainless steel commingled yarn’, Textile Research Journal, 2003, 74, 4, 322–326. [8] Pomfret S J, Adams P N, Comfort N P and Monkman A P, ‘Advances in processing routes for conductive polyaniline fibers’, Synthetic Metals, 1999, 101, 1–3, 724–725. [9] Cakmak G, Kucukyavuz Z and Kucukyavuz S, ‘Conductive copolymers of polyaniline, polypyrrole and poly(dimethylsiloxane)’, Synthetic Metals, 2005, 151, 1, 10–18. [10] Kim B, Koncar V, Devaux E, Dufour C and Viallier P, ‘Electrical and morphological properties of PP and PET conductive polymer fibers’, Synthetic Metals, 2004, 146, 2, 167–174. [11] Hancock J G and Baker R E, ‘Bi-component electrically conductive drawn polyester fiber and method for making same’, US patent 20080226908, 2008. [12] Sharon M, ‘Carbon nanomaterials’, Encyclopedia of Nanoscience and Nanotechnology, American Scientific Publishers, Valencia, CA, 2004, 1, 517–546. [13] Meyyappan M, Carbon Nanotubes: Science and Applications, Taylor & Francis, London, 2005. [14] Laxminarayana K and Jalili N, ‘Functional nanotube-based textiles: pathway to next generation fabrics with enhanced sensing capabilities’, Textile Research Journal, 2005, 75, 9, 670–680. [15] Gommans H H, Alldredge J W, Tashiro H, Park J, Magnuson J and Rinzler A G, ‘Fibers of aligned single-walled carbon nanotubes: polarized Raman spectroscopy’, Journal of Applied Physics, 2000, 88, 2509–2514. © Woodhead Publishing Limited, 2010
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[16] Vigolo B, Pénicaud A, Coulon C, Sauder C, Pailler R, Journet C, Bernier P and Poulin P, ‘Macroscopic fibers and ribbons of oriented carbon nanotubes’, Science, 2000, 290, 1331–1334. [17] Baughman R H, Zakhidov A A and Heer W A D, ‘Carbon nanotubes – the route toward applications’, Science, 2002, 297, 5582, 787–792. [18] Xue P, Park K H, Tao X M, Chen W and Cheng X Y, ‘Electrically conductive yarns based on PVA/carbon nanotubes’, Composite Structures, 2007, 78, 271–277. [19] Davis V A and Pasquali M, ‘Macroscopic fibers of single-wall carbon nanotubes’, in Schulz M J, Kelkar A D and Sundaresan M J, eds, Nanoengineering of Structural, Functional and Smart Materials, Vol. 1, Part 3, Chapter 11, pp. 259–279, CRC Press, Boca Raton, FL. [20] Haggenmueller R, Gommans H H, Rinzler A G, Fischer J E and Winey K I, ‘Aligned single-wall carbon nanotubes in composites by melt processing methods’, Chemical Physics Letters, 2000, 330, 219–225. [21] Jiang K, Li Q and Fan S, ‘Nanotechnology: Spinning continuous carbon nanotube yarns’, Nature, 2002, 419, 801. [22] Atkinson K R, Hawkins S C, Huynh C, Skourtis C, Dai J, Zhang M, Fang S, Zakhidov A A, Lee S B, Aliev A E, Williams C D and Baughman R H, ‘Multifunctional carbon nanotube yarns and transparent sheets: Fabrication, properties, and applications’, Physica B, 2007, 394, 339–343. [23] Lobovsky A, Morris R C, Kozlov M, Zakhidov A, Matrunich J and Baughman R H, ‘Spinning, processing and applications of carbon nanotube filaments, ribbons and yarns’, US Patent 6682677, 2004. [24] ‘Nanotube yarns and forests’, Science, 2004, 306, 5700, 1255a. [25] Li Y L, Kinloch I A and Windle A H, ‘Direct spinning of carbon nanotube fibers from chemical vapor deposition synthesis’, Science, 2004, 304, 5668, 276–278. [26] Zhang X, Jiang K, Feng C, Liu P, Zhang L, Kong J, Zhang T, Li Q and Fan S, ‘Spinning and processing continuous yarns from 4-inch wafer scale super-aligned carbon nanotube arrays’, Advanced Materials, 2006, 18, 12, 1505–1510. [27] Li Q W, Zhang X F, DePaula R F, Zheng L X, Zhao Y H, Stan L, Holesinger T G, Arendt P N, Peterson D E and Zhu Y T, ‘Sustained growth of ultralong carbon nanotube arrays for fiber spinning’, Advanced Materials, 2006, 18, 23, 3160–3163. [28] Shim B S, Chen W, Doty C, Xu C and Kotov N A, ‘Smart electronic yarns and wearable fabrics for human biomonitoring made by carbon nanotube coating with polyelectrolytes’, Nano Letters, 2008, 8, 12, 4151–4157. [29] Fugetsu B, Akiba E, Hachiya M and Endo M, ‘The production of soft, durable, and electrically conductive polyester multifilament yarns by dye-printing them with carbon nanotubes’, Carbon, 2009, 47, 527–544. [30] Paul C R, Introduction to EMC, Wiley, New York, 1992. [31] Chen H C, Lee K C, Lin J H and Koch M, ‘Comparison of electromagnetic shielding effectiveness properties of diverse conductive textiles via various measurement techniques’, Journal of Materials Processing Technology, 2007, 192–193, 549– 554. [32] Chen H C and Lin J H, ‘Electromagnetic shielding effectiveness of copper/stainless steel/polyamide fiber co-woven-knitted fabric reinforced polypropylene composites’, Journal of Reinforced Plastics and Composites, 2008, 2, 2. [33] Berglin L, ‘Design of a flexible textile system for wireless communication’, Proceedings of the 5th AUTEX Conference, Portorož, Slovenia, 2005, 27–29 June. © Woodhead Publishing Limited, 2010
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[34] Hertleer C, Tronquo A, Rogier H and Langenhove L V, ‘The use of textile materials to design wearable microstrip patch antennas’, Textile Research Journal, 2008, 78, 8, 651–658. [33] Coosemans J, Hermans B and Puers R, ‘Integrating wireless ECG monitoring in textiles’, Sensors and Actuators, 2006, 130, 131, 48–53. [36] Zi˛eba J and Frydrysiak M, ‘Textronics – electrical and electronic textiles. Sensors for breathing frequency measurement’, Fibres & Textiles in Eastern Europe, 2006, 14, 5, 43–48. [37] Rattfalt L, Linden M, Hult P, Berglin L and Ask P, ‘Electrical characteristics of conductive yarns and textile electrodes for medical applications’, Medical and Biological Engineering and Computing, 2007, 45, 1251–1257. [38] Choi S and Jiang Z, ‘A wearable cardiorespiratory sensor system for analyzing the sleep condition’, Expert Systems with Applications, 2008, 35, 317–329. [39] Westbroek P, Priniotakis G, Palovuori E, Clerck D K, Langenhove V L and Kiekens P, ‘Quality control of textile electrodes by electrochemical impedance spectroscopy’, Textile Research Journal, 2006, 76, 2, 152–159. [40] Lai K, Sun R J, Chen M Y, Wu H and Zha A X, ‘Electromagnetic shielding effectiveness of fabrics with metallized polyester filaments’, Textile Research Journal, 2007, 77, 4, 242–246. [41] Jung S R, Yong S C, Tae J K and Sang W N, ‘Electromagnetic shielding effectiveness of multifunctional metal composite fabrics’, Textile Research Journal, 2008, 78, 825. [42] Kathirgamanathan P, Toohey M J and Haase J, ‘Measurements of incendivity of electrostatic discharges from textiles used in personal protective clothing’, Journal of Electrostatics, 2005, 49, 51–70. [43] Tappura K and Nurmi S, ‘Computational modeling of charge dissipation of fabrics containing conductive fibers’, Journal of Electrostatics, 2003, 58, 117–133. [44] Xie J and Tamaki J, ‘An experimental study on discharge mediums used for electrocontact discharge dressing of metal-bonded diamond grinding wheel’, Journal of Materials Processing and Technology, 2008, 208, 239–244. [45] Kitajima N, Ueda K, Ohshima T and Sato M, ‘Development of textile electrode for microbial inactivation with pulsed electric field’, Textile Research Journal, 2007, 77, 7, 528–534. [46] Rock M, ‘Electric heating/warming fabric articles’, US Patent 7268320, 2007. [47] Rock M, ‘Electric heating/warming fabric articles’, US Patent 7202443, 2007. [48] Wu M L, ‘Electrically conductive and heating wire containing fabric’, US Patent 6897408, 2005. [49] Payvandy P, Latifi M and Agha-Mirsalim M, ‘Interlacing metallic filaments by rotational permanent magnetic field’, Fibers and Polymers, 2008, 9, 5, 583–587. [50] Payvandy P, Latifi M, Agha-Mirsalim M and Moghani J S, ‘Rotational electromagnetic field-aided false twisting of metallic filaments’, Journal of the Textile Institute, in press. [51] Yousefzadeh-Chimeh M, Latifi M, Amani M and Jalili N, ‘Next generation fabrics by fabrication of carbon nanotube/pan electrospun nanofiber with special properties’, Iran-Indian Joint Conference on Nanotechnology, Tehran, Iran, 27–29 April 2008. [52] Yousefzadeh-Chimeh M, Latifi M, Amani M and Jalili J, ‘Direct yarn formation from electro-spun cnt/pan composite nano-fiber’, 2nd International Congress on Nano-science and Nanotechnology, Tabriz, Iran, 28–30 October 2008.
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11
High modulus, high tenacity yarns
H. H u and Y. L i u, The Hong Kong Polytechnic University, Hong Kong
Abstract: This chapter is intended to provide an introduction to high modulus, high tenacity (HM-HT) fibers and their commercialized yarn products. For inorganic fibers, glass, ceramic and basalt fibers and their yarns are presented. For carbon fibers, three kinds of carbon fibers made from different precursors, i.e., rayon, PAN and pitch, are presented. For organic polymeric HM-HT fibers, aramid and high performance polyethylene are presented. For each kind of HM-HT fiber, the content includes the following parts: fiber structure and chemical composition, yarn forms, fiber and yarn properties, applications and future trends. Key words: high modulus, high tenacity, yarn, glass, carbon, aramid.
11.1
Introduction
High modulus, high tenacity (HM-HT) yarns are those made from HM-HT fibers. Fibers which have both tenacity above 3 GPa and modulus above 50 GPa are considered as HM-HT fibers [1]. Many HM-HT fibers found in practical applications have a modulus above 50 GPa, but their tenacity is normally under 3 GPa. For this reason, the HM-HT fibers presented in this chapter normally may have a tenacity smaller than 3 GPa. HM-HT fibers can be classified into three categories: inorganic fibers, quasiorganic fibers and polymeric fibers. For inorganic fibers, the high strength and modulus are achieved from their inorganic 3-D networks. Carbon fibers may be described as quasi-organic fibers, because they result from organic chemistry. The turbostratic form of the hexagonal planar network of carbon atoms would give the high strength and stiffness. HM-HT polymeric fibers are formed with high orientation of macromolecular chains along the fiber axis. This chapter is intended to provide an introduction to HM-HT fibers and their commercialized yarn products. The contents are organized according to the above classification. For the inorganic fibers, glass, ceramic and basalt fibers and their yarns are presented. For the carbon fibers, three kinds of carbon fibers made from different precursors, i.e., rayon, PAN and pitch, are presented. For the organic polymeric HM-HT fibers, aramid and high performance polyethylene are presented. For each kind of HM-HT fiber, the 329 © Woodhead Publishing Limited, 2010
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content includes the following parts: fiber structure and chemical composition, yarn forms, fiber and yarn properties, applications and future trends. Many tables are also used to provide maximum possible information.
11.2
Glass fibers and yarns
11.2.1 Composition and structure Glass fibers are made from extremely fine fibers of glass based on silica [2]. High strength glass fibers are from aluminosilicates attenuated at higher temperatures into fine fibers ranging from 5 to 24 mm. A typical range of the chemical compositions for different types of commercially available glass fibers is given in Table 11.1 [3,4]. The nomenclature and specific applications of different types of glass fibers are shown in Table 11.2. Glassy materials are amorphous, having no crystallinity or long-range order. In high performance glass fibers, silica forms a three-dimensional network of Si–O bonds from the fundamental building-block of [SiO4]4– tetrahedra [5]. The two-dimensional representation of a simplified glass structure is shown in Fig. 11.1. The amorphous silica component is as an interconnected network of silicon and oxygen atoms.
11.2.2 Properties The properties of different types of glass fibers listed in Table 11.1 are presented in Tables 11.3–11.6. So some general structure–property relationships can be determined by comparing Table 11.1 with Tables 11.3–11.6. Physical properties Densities are directly related to the atomic weights of the glass components in a specific composition. ASTM C 693 is a frequently used method for density determinations [6]. The glass fiber densities range from approximately 2.11 g/cm3 for D-glass to 2.72 g/cm3 for ECR glass. The softening point in Table 11.3 is the temperature at which the glass readily flows under its own weight, and the strain point is identical to the glass transition temperature [3]. When comparing with Table 11.1, it can be seen that more tetravalent silicon leads to higher glass transition temperature glasses. A typical E-glass fiber can have strength of 3 GPa. However, the respective strand strengths are normally 20 to 30% lower than the values reported in Table 11.3 due to surface defects introduced during the strand-forming process [3]. In addition, the strength of glass fibers decreases when the fibers are exposed to increasing temperature. For example, E-glass and S-2 glass fibers have been found to retain approximately 50% of their room-temperature strength at 538°C. The
© Woodhead Publishing Limited, 2010
Table 11.1 Composition ranges (%) for commercial glass fibers No boron E-glass
SiO2 59–62 63–72 64–68 72–75 52–56 54–62 55–75 55–65 64–66 52–62 Al2O3 12–15 0–6 3–5 0–1 12–16 9–15 0–5 15–30 24–25 12–16 B2O3 <0.2 0–6 4–6 21–24 5–10 0–8 CaO 20–24 6–10 11–15 0–1 16–25 17–25 1–10 9–25 0–0.18 16–25 MgO 1–4 0–4 2–4 0–5 0–4 3–8 9.5–10.2 0–5 ZnO 2–5 BaO 0–1 Li2O 0–1.5 Na2O+K2O 14–16 7–10 0–4 0–2 0–2 11–21 0–1 0–0.2 0–2 TiO2 0–0.6 0–1.5 0–4 0–12 0–1.5 ZrO2 1–18 Fe2O3 0–0.5 0–0.8 0–0.3 0–0.8 0–0.8 0–5 0–0.1 0–0.8 F2 0–0.4 0–1 0–5 0–0.3 0–1 Source: Ref. 3.
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Oxide Advantex® A-glass C-glass D-glass E-glass ECR-glass AR-glass R-glass S-2-glass
331
332
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Glass fiber
Material
®
Advantex Calcium aluminosilicate glass AR-glass Alkali resistant glasses C-glass Calcium borosilicate glasses D-glass Borosilicate glasses E-glass Alumina–calcium–borosilicate glasses ECR-glass Calcium aluminosilicate glasses R-glass Calcium aluminosilicate glasses S-glass Magnesium aluminosilicate glasses Source: authors’ summary.
Specific applications A boron-free substitute for E-glass, providing ECR-glass acid resistance with the reinforcing characteristics of E-glass Used in cement and concrete Used for their exceptional stability in acidic environments Radomes and other specialty applications requiring permeability to electromagnetic waves Strength and high electrical resistivity Acid corrosion resistivity, strength and electrical resistivity Higher strength and temperature resistance High strength, modulus and durability under conditions of extreme temperature of corrosive environments
Technical textile yarns
Table 11.2 Nomenclature and specific applications of glass fibers
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333
Silicon Oxygen Sodium Chemical bonds
11.1 Schematic diagram of glass networks (reproduced from Ref. 2).
modulus is very much dominated by the chemical forces operating within the amorphous inorganic glass and has a value of around 70–80 GPa. In contrast to the strength, the modulus of glass fiber gradually increases as the fiber is heated. For example, the Young’s modulus of E-glass fibers that have been annealed to compact their atomic structure will increase from 72 GPa to 84.7 GPa [3]. Chemical resistance The chemical resistance of glass fibers to the corrosive and leaching actions of acids, bases, and water is expressed as a percent weight loss. The data listed in Table 11.4 are obtained from the percentage weight loss of 10 micron diameter pristine glass fibers put into corrosive solution held at 96°C. Basically, the chemical resistance of glass fibers depends on the compositions and diameter of the fibers, the corrosive solution, the exposure time, the solution volume to glass mass ratio and other factors. In water, the weight loss is proportional to the amount of highly soluble cations (B, Na, and K) in the glass [5]. In an acid, removal of cations other than silicon begins rapidly, but slows down as a barrier of leached glass is formed [7]. In a base, weight loss measurements are more subjective as the alkali affects the network and reprecipitates the metal oxides [5]. Tensile strength after
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Property Advantex® A-glass C-glass D-glass E-glass ECR-glass AR-glass R-glass S-2-glass
No boron E-glass
Density, g/cm3 2.624 2.44 2.52 2.11–2.14 2.58 2.72 2.70 2.54 2.46 Refractive index 1.561 1.538 1.533 1.465 1.558 1.579 1.562 1.546 1.521 Softening point, °C (°F) 705 750 771 846 882 773 952 1056 (1300) (1382) (1420) (1555) (1619) (1424) (1745) (1932) Annealing point, °C (°F) 588 521 657 816 (1090) (970) (1215) (1500) Strain point, °C (°F) 691 522 477 615 736 766 (1025) (890) (1140) (1357) (1410) Tensile strength, MPa: –196°C 5380 5310 5310 8275 23°C 3310 3310 2415 3445 3445 3241 4135 4890 371°C 2620 2165 2930 4445 538°C 1725 1725 2140 2415 Young’s modulus, GPa: 23°C 68.9 68.9 51.7 72.3 80.3 73.1 85.5 86.9 538°C 81.3 81.3 88.9 Elongation, % 4.8 4.8 4.6 4.8 4.8 4.4 4.8 5.7
2.62 1.561 9161
Source: Ref. 3.
7361 691
3450
80.5 4.6
Technical textile yarns
Table 11.3 Physical properties of commercial glass fibers
Table 11.4 Chemical properties of commercial glass fibers (weight loss over 24 and 168 hours) Durability (% weight loss) 24 168 24 168 24 168 24 168
h 1.8 h 4.7 h 1.4 h h 0.4 h 2.3 h h
C-glass
D-glass
E-glass
ECR-glass
1.1 2.9 4.1 7.5 2.2 4.9 24 31
0.7 5.7 21.6 21.8 18.6 19.5 13.6 36.3
0.7 0.6 0.9 0.7 42 5.4 43 7.7 39 6.2 42 10.4 2.1 2.1 1.8
AR-glass
R-glass
0.7 0.4 1.4 0.6 2.5 9.5 3.0 10.2 1.3 9.9 5.4 10.9 1.3 3.0 1.5
S-2-glass 0.5 0.7 3.8 5.1 4.1 5.7 2.0 2.1
Source: Ref. 3.
Table 11.5 Electrical properties of commercial glass fibers Property
A-glass
C-glass
D-glass
Dielectric constant 1 MHz 6.2 6.9 3.8 10 GHz 4.0 Dissipation factor 1 MHz 0.0085 0.0005 10 GHz 0.0026 Volume resistivity (ohm-cm) 1.0E+10 Surface resistivity (ohms) Dielectric strength (volts/mil)
E-glass
ECR-glass
AR-glass
R-glass
6.6 6.1 0.0025 0.0038 4.02E+14 4.20E+15 262
6.9 8.1 6.4 7.0 0.0028 0.0034 0.0031 0.0051 3.84E+14 2.03E+14 1.16E+16 6.74E+13 250 274
S-2-glass 5.3 5.2 0.0020 0.0068 9.05E+12 8.86E+12 330
High modulus, high tenacity yarns
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H2O 10% HCl 10% H2SO4 10% Na2CO3
A-glass
Source: Ref. 3.
335
336
Property
A-glass
C-glass
D-glass
E-glass
ECR-glass AR-glass R-glass
Specific heat, J/g°C (BTU/lb°F): 23°C 0.796 (0.190) 0.787 (0.188) 0.733 (0.176) 0.810 (0.193) 0.732 200°C 0.900 (0.215) 1.03 (0.247) 0.97 (0.232) 0.938 Thermal expansion coefficient (¥ 10–7), /°C (°F): –30°C to 250°C 73 (41) 63 (35) 25 (14) 54 (30) 59 (33) 65 (36) 33 (18) Source: Ref. 3.
S-2-glass 0.737 (0.176)
16 (8.9)
Technical textile yarns
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Table 11.6 Thermal properties of commercial glass fibers
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337
corrosion is a better indicator of the residual glass fiber properties, typical results of E- and S-glass for 24-hour exposure at 96°C being shown in Fig. 11.2. It is clear that S-glass fibers show no decrease in strength from pH 1 to pH 11, whereas E-glass fibers degrade in strength significantly either above or below a pH of 6. Electrical properties The electrical properties are listed in Table 11.5. The values show that there are no significant differences for each kind of fiber. Actually, D- and E-glass fibers were specifically developed for cost-effective and high electrical insulation performance as well as dielectric properties. D-glass fibers are made from borosilicate glasses with low dielectric constant. They are used for radomes and other specialty applications requiring permeability to electromagnetic waves. E-glass fibers are made from alumina–calcium–borosilicate glasses with maximum alkali content of 2% w/w. They are used as general-purpose reinforcement where strength and high electrical resistivity are required. Thermal properties The thermal properties of glass fibers such as specific heat and thermal expansion are listed in Table 11.6. It is obvious that the thermal properties are significantly different for each type of fiber. Above the transition temperature, no further increase in specific heat was observed. The expansion measurements were made on annealed bars using ASTM D 696 [8]. A lower
Tensile strength (GPa)
S-2 glass® E glass 4.2
2.1
0
0
1
2
3 4 5 6 7 8 9 10 pH Buffer (24 hours at 205°F exposure)
11
11.2 Tensile strength after corrosion is a better indicator of the residual glass fiber properties (source: Ref. 3).
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coefficient of thermal expansion (CTE) in the high strength glasses allows higher dimensional stability at temperature extremes.
11.2.3 Commercial products of glass yarns Glass fibers are made from molten glass. The viscous liquid is drawn through tiny holes at the base of the furnace to form continuous filaments. Once the continuous glass fibers have been produced, they need to be converted into a suitable product form for their intended applications. The major yarn forms for glass fibers are rovings, continuous filament yarns, textured yarns, folded yarns and cabled yarns. The processing of these yarns is shown in Figs. 11.3 and 11.4. Rovings Roving is defined as a multiplicity of filaments or yarns gathered together into an approximately parallel arrangement without twist by ASTM D 578 [9]. Direct-winding rovings are used in their original continuous form in filament
Furnace
Batch house Forming package
Bushing filaments sizing
Twisting
Oven
Customer Rovings
Customer Continuous filament yarns Customer Textured yarns
Air jet
11.3 Simplified schematic diagrams depicting some of the many different product consolidation steps.
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Single Folded Cabled
11.4 Simplified schematic diagram of single, folded and cabled yarns.
winding and pultrusion process. They are easy to unwind with an even tension, very low fuzz generation during processing, outstanding processing behavior and superior wettability. Rovings are the most widespread commercial form and many manufacturers produce these products. The yield of the finished roving is determined by the number of input ends and the yield of the input strand or sliver. Final package weight and dimensions of rovings can be made to vary widely for the required end-use. Table 11.7 lists some of the designation and technical data of glass rovings extracted from manufacturers’ data sheets. The package dimensions are illustrated in Fig. 11.5. Due to the advantages of rovings, they are used in many applications. They can be processed into unidirectional reinforced composites through filament winding or pultrusion, woven into various fabrics, or chopped into short lengths for spraying directly into a mold with the resin or for deposition with the resin into a secondary molding product such as DMC, BMC or SMC. Continuous filament yarns Rovings are assembled at the bushing. They are generally used for advanced composites where the memory of the tows is a distinct disadvantage and where twists need to be absent. Continuous filament yarns are produced by twisting and plying strands with varying levels of rovings. They are defined by ASTM D 578 as a yarn made of filaments that extend substantially throughout the length of the yarn [9]. A twist is mechanically applied to yarns because in addition to helping keep all of the filaments together, it provides the yarn with higher abrasion resistance, easier processing, and better tensile strength. The twist process could provide additional integrity to the yarn before it is subjected to subsequent processes such as weaving and knitting. The two types of twist normally used are known as S and Z, which indicate the direction in which the twisting is performed [10]. Table 11.8 lists some of the designation and technical data of glass continuous filament yarns extracted from manufacturers’ data sheets. The yarn nomenclature of the SI system is best explained by an example, here for a product named EC5-11 1 ¥ 0 Z40:
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Company Designation Glass type
Linear LOI density, content, tex %
Filament diameter, mm
JMa JM JM JM JM JM AGYb AGY
300 410 1200 2400 300 410 406 2033
13.5 0.15 15.5 0.15 16 0.15 16 0.15 13 0.15 15 0.15 9 9
a
PR80 300 076 PR 80 410 076 PR 220 1200 908 PR 440 2400 908 PR 80 300 851 PR 80 410 851 365-AA-1250 365-AA-250
E E E E E E S S
0.45 0.45 0.6 0.6 0.45 0.45 0.5 0.5
Johns Manville, Inc. AGY, Inc. Source: reprinted from manufacturer’s technical literature. b
Moisture Inside content diameter maximum (I.D.), cm 16 16 16 16 16 16 7.6 7.6
Outside Traverse Tube diameter (T) length (O.D.), cm (L)
Weight, kg
30 30 30 30 30 30 17.8 17.8
20 20 20 20 20 20 6.8 6.8
25.5 25.5 25.5 25.5 25.5 25.5 25.4 27.7 25.4 27.7
Technical textile yarns
Table 11.7 Designation and technical data of glass rovings
High modulus, high tenacity yarns
341
O.D. I.D.
L
T
(a)
(b)
11.5 Package dimensions of glass roving.
Table 11.8 Designation and technical data of glass continuous filament yarns Yarn designation
Nominal twist, tpm
Z
S
EC5 2.75 1 ¥ 0 20–40 EC5 2.75 1 ¥ 2 152–176 EC5 5.5 1 ¥ 0 20–40 EC5 11 1 ¥ 0 20–40 EC6 16 1 ¥ 0 20–40 EC5 5.5 1 ¥ 3 152–176 EC5 11 1 ¥ 2 340 EC5 11 1 ¥ 3 340 EC5 22 1 ¥ 2 340 EC7 22 2 ¥ 0 160–200 EC11 45 1 ¥ 0 20–40 EC6 50 1 ¥ 0 20–40 EC7 22 3 ¥ 0 120–160 EC3.5 33 2 ¥ 0 80–120 EC4.5 66 1 ¥ 0 80–120 EC6 33 1 ¥ 3 112–152 EC5 11 3 ¥ 4 152–176 EC6 33 2 ¥ 2 112–152 EC13 66 2 ¥ 0 120–160 EC6 134 1 ¥ 0 20–40 EC9 134 1 ¥ 0 40–80 EC9 66 2 ¥ 4 112–152 EC9 33 4 ¥ 5 100–140 EC9 33 4 ¥ 6 100–140 EC9 33 4 ¥ 7 100–140
Approximate yarn number 2.75 5.5 5.5 11 16 16.5 22 33 44 44 45 50 66 66 66 99 132 132 132 134 134 530 660 795 925
Source: reprinted from manufacturer’s technical literature.
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Breaking strength, N 1.1 2.2 4.9 8.0 8.0 9.8 17.3 21.4 21.4 18.2 17.8 29.4 35.6 25.4 46.7 58.7 50.7 49.8 49.8 203 285 342 399
342
Technical textile yarns
∑ E = electrical glass formulation ∑ C = continuous filaments ∑ 5 = filament diameter (see ASTM D 578) ∑ 11 = 11 g per 1000 m of yarn ∑ 1 ¥ 0 = single yarn end ∑ Z40 = 40 z twists per meter (TPM). These yarns are used for further fabrication, typically warping and weaving for glass fabrics and tapes. Textured yarns Textured glass yarn is a yarn processed from continuous filament yarn in such a manner as to induce bulk to the yarn by disorientation of the filaments. Textured yarns can be produced by several types of process. Usually, the yarn is subjected to an air jet that impinges on its surface to make the yarn ‘fluffy’ as shown in Fig. 11.3. Such yarns can be made starting either from a single strand or from two or more strands in which one or all have been ‘opened’ to give the ‘bulky’ aspect of textured yarn. For many applications, glass yarns are textured in order to gain increased bulkiness, porosity, softness and elasticity in some situations. Texturing is suitable for production of special technical glass fabrics for insulation, shielding and sealing applications. The texture process allows the resin-to-glass ratio to be increased in the final composite. Table 11.9 lists some of the designation and technical data of textured glass yarns extracted from manufacturers’ data sheets. Folded yarns In order to obtain special yarn features, particularly high strength and modulus for technical and industrial applications, folded yarns are often needed, also named plied yarns. Folded yarns are two or more single continuous filament yarns that have been combined by twisting and plying strands of fiber in a second twisting operation as shown in Fig. 11.4. This technique is also known as twisting. This is carried out to vary the strength, diameter and flexibility of the yarn to meet special requirements. Table 11.10 lists some of the designation and technical data of folded glass yarns extracted from manufacturers’ data sheets. These yarns are used for further fabrication, typically warping and weaving for glass fabrics and tapes. Cabled yarns Cabled yarn is also called rope or cord and is formed by twisting together two or more folded yarns or a combination of folded and single yarns, as shown in Fig. 11.4. Glass cabled yarns are extremely strong, resilient, and © Woodhead Publishing Limited, 2010
Table 11.9 Designation and technical data of glass textured yarns Glass type
JM JM JM JM JM JM JM JM AGY AGY AGY AGY AGY
E 0.6 0.20 E 0.6 0.20 E 0.4 0.20 E 0.4 0.20 E 0.4 0.20 E 0.6 0.20 E 0.6 0.20 E 0.6 0.20 E E E E E
TH 690 056R SJ TH 1200 056R TH 1200 126 TH 2400 126 TH 5000 126 TH 215/1 056 (9) SJ TH 390/1 056R (9) SJ TH 660/1 056R (11) SJ EC6-136 1 ¥ 0 Z20 EC6-99 1 ¥ 0 Z28 EC6-68 1 ¥ 0 Z20 EC6-50 1 ¥ 0 Z28 EC9-134 1 ¥ 0 Z12
LOI content, %
Source: reprinted from manufacturer’s technical literature.
Moisture content maximum, %
Linear density, yield/tex
Filament diameter, Tensile strength mm minimum, N
718/690 11 413/1200 11 413/1200 12.5 206/2400 12.5 99/5000 12.5 2306/215 9 1272/390 9 751/660 11 125.9–143.4 93.6–105.5 61.8–71.1 46.8–52.8 127.1–141.9
20 100 200 350 450 3.5 10 15 49.8 35.6 25.4 19.1 49.8
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Company Designation
343
344
Technical textile yarns
Table 11.10 Designation and technical data of glass folded yarns Designation Sizing Filament count Yarn diameter, Twist tolerance, mm tpm EC433 1 ¥ 0 Z40 EC433 1 ¥ 0 Z120 EC433 2 ¥ 0 Z120 EC433 4 ¥ 0 Z120 EC5-11 1 ¥ 0 Z40 EC5-11 1 ¥ 0 Z40 EC5-11 1 ¥ 0 Z40 EC5-11 1 ¥ 0 Z40 EC5-5.5 1 ¥ 0 Z40 EC5-5.5 1 ¥ 0 Z40 EC5-2.8 1 ¥ 0 Z40 EC5-2.8 1 ¥ 0 Z40 EC6-136 1 ¥ 0 Z40 EC6-68 1 ¥ 0 Z28 EC6-50 1 ¥ 0 Z28 EC6-34 1 ¥ 0 Z28
636 636 636 636 620-1 622 620-1 622 620-1 622 620-1 622 636 620 636 620
988 988 2128 4256 204 204 204 204 102 102 51 51 1632 816 600 408
0.203 0.203 0.246 0.348 0.122 0.122 0.122 0.122 0.085 0.085 0.066 0.066 0.0396 0.269 0.249 0.203
±12 ±24 ±24 ±24 ±12 ±12 ±12 ±12 ±12 ±12 ±12 ±12 ±12 ±8 ±8 ±8
Source: reprinted from manufacturer’s technical literature.
flexible. For mostly common cabled yarns, the fibers are arranged in helical structures whose axes form helices in larger structures, the process continuing in stages until a rope is complete [11]. Either twisting or interlacing braiding techniques are used to arrange and contain the cabled elements. Table 11.11 lists some of the designation and technical data of glass cabled yarns extracted from manufacturers’ data sheets. They have wide applications in the following fields: automotive (passenger cars and commercial vehicles), textile machinery (spinning, weaving and plying machines), laundry equipment (washing machines, dryers), household appliances (food mixers, slicers, power tools), agriculture/horticulture (combine harvesters, lawn mowers, edge trimmers), office equipment (computer printers, typewriters, copiers) and handling equipment (hoists, door movements, seat adjusters).
11.2.4 Applications A number of types of glass fibers are produced with different compositions according to the desired characteristics. Glass fibers have applications in a vast array of markets such as automotive, aerospace, marine, civil construction, sporting goods and electrical/electronics.
11.2.5 Future trends Any product that is environmentally friendly is bound to be accepted by the industry over a period of time. ECR glass fibers, with the added advantages
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Table 11.11 Designation and technical data of glass cabled yarns Designation Initial twist, Final twist, Weight, Diameter, Tensile Ultimate tpm tpm g/1000 m mm strength, elongation, kg % EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9 EC9
34. 3/0 34. 3/3 80 34. 3/5 80 34. 3/8 80 34. 3/11 80 34. 3/13 80 68. 1/2 98 68. 1/2 197 110. 1/0 110. 1/0 110. 1/0 110. 1/2 142 110. 1/3 142 110. 1/3 142 110. 1/6 83 110. 1/10 83 110. 1/10 83 110. 1/11 83 110. 1/13 83 110. 1/14 83 140. 1/0 140. 1/3 79 140. 1/3 142 140. 1/7 79 140. 1/10 83 140. 3/6 79 140. 3/12 79
142 118 118 80 80 80 98 98 59 142 165 142 142 236 83 83 118 83 83 83 98 83 142 83 83 39 39
135 400 675 1075 1480 1750 168 168 135 135 135 270 400 410 800 1350 1350 1500 1775 1910 173 520 520 1210 1750 3150 6350
0.23 0.50 0.70 0.85 1.12 1.22 0.34 0.34 0.23 0.23 0.23 0.45 0.55 0.55 0.80 1.05 1.05 1.10 1.20 1.25 0.29 0.63 0.63 0.95 1.20 1.75 2.47
8 27 45 75 95 115 12 11 9 8 8 18 26 25 50 80 80 85 105 110 11 33 33 70 105 150 300
2.5 2.5 2.6 2.6 2.6 2.6 2.8 2.8 2.8 2.8 2.8 2.8 3.1 2.8 2.5 2.8 2.8 2.8 3.1 3.2 3.2
Source: reprinted from manufacturer’s technical literature (NGF Europe Ltd).
of significantly superior acid resistance, better electrical properties, higher tensile properties in pultrusion and higher temperature resistance can effectively replace E-glass. Environmentally friendly, boron-free ECR glass fibers may be the future trends.
11.3
Carbon fibers and yarns
11.3.1 Composition and structure Carbon fibers refer to fibers which are at least 92 wt% carbon in composition. The carbon atoms are bonded together in microscopic crystals that are more or less aligned parallel to the long axis of the fiber. The crystal alignment makes the fiber very strong for its size. The atomic structure of carbon fiber is similar to that of graphite,
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Technical textile yarns
consisting of sheets of carbon atoms (graphite sheets) arranged in a regular hexagonal pattern. The difference lies in the way these sheets interlock. Graphite is a crystalline material in which the sheets are stacked parallel to one another in regular fashion. The intermolecular forces between the sheets are relatively weak van der Waals forces, giving graphite its soft and brittle characteristics. Depending upon the precursor to make the fiber, carbon fiber may be turbostratic [12] (Fig. 11.6) or graphitic, or have a hybrid structure with both graphitic and turbostratic parts present. In turbostratic carbon fiber the sheets of carbon atoms are haphazardly folded, or crumpled, together. Carbon fibers derived from polyacrylonitrile (PAN) are turbostratic, whereas carbon fibers derived from mesophase pitch are graphitic after heat treatment at temperatures exceeding 2200°C. Turbostratic carbon fibers tend to have high tensile strength, whereas heat-treated mesophase-pitch-derived carbon fibers have high Young’s modulus and high thermal conductivity. Carbon fibers consist almost exclusively of carbon atoms. Almost all commercial carbon fibers are produced by first converting a carbonaceous precursor into fiber form. Precursors for carbon fibers include cellulosic rayon, polyacrylonitrile (PAN) and pitch. The precursor fiber then is crosslinked in order to render it infusible. Finally, the crosslinked precursor fiber is heated at temperatures from 1200 to about 3000°C in an inert atmosphere to drive off nearly all of the non-carbon elements, converting the precursor to a carbon fiber. Based on precursor fiber materials, carbon fibers are classified into rayon-based carbon fibers, PAN-based carbon fibers, pitch-based carbon fibers, mesophase pitch-based carbon fibers and isotropic pitch-based carbon fibers.
11.6 Irregular stacking of aromatic sheets: turbostratic carbon (reproduced from Ref. 12).
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11.3.2 Properties Attractive properties of carbon fibers include low density, high tensile modulus and strength, low thermal expansion coefficient, thermal stability in the absence of oxygen to over 3000°C, excellent creep resistance, chemical stability, biocompatibility, high thermal conductivity, low electrical resistivity, and availability in a continuous form. The properties of carbon fiber are quite dependent on the structure, in particular, the crystallite size as defined by the coherent length perpendicular and parallel to the carbon layers. Young’s modulus is an intrinsic property and is governed by the orientation of the graphitic crystallites relative to the fiber axis. The lower this angle, the greater is the modulus. As the quality of the PAN precursor has been improved and its diameter reduced, this has enabled carbon fibers to be produced with higher strengths, with a diameter of about 5 mm. The smaller the carbon fiber diameter, the greater is the strength. Mechanical properties Up to now, there are three types of carbon fibers available in the world market. The first commercial carbon fibers were based on viscose rayon, a cellulosic precursor, but Polycarbon is now the only current producer of this type of carbon fiber. The properties of rayon-based carbon fibers are listed in Table 11.12. The most commonly used carbon fibers are based on PAN and pitch. Their physical properties are listed in Tables 11.13 and 11.14, respectively. Figure 11.7 shows a plot of the strength versus modulus drawn using the data from Tables 11.12–11.14. At the present time, the ratio of tensile strength to Young’s modulus for the commercial carbon fibers in Fig. 11.7 is in the range 0.0026–0.024. Torayca T1000G [13], having the highest strength, 6.37 GPa, among commercial carbon fibers, exhibits a strength-to-modulus ratio of 0.022. It also can be seen that PAN-based carbon fibers have higher strength and pitch-based carbon fibers have higher modulus. Cellulose-based carbon fibers have both lower strength and lower modulus. The modulus of PAN-based fibers can be increased by heat treatment, though the strength decreases. In fact, the tensile modulus of carbon fibers can be determined mainly by the carbonization/graphitization temperature. In addition, the nature of precursors (PAN, rayon, pitch) affects the ease of reaching a certain level modulus. Manufacturers have always been keen to develop higher strength carbon fiber with adequately designed modulus. The tensile stress–strain curve of carbon fibers can be considered to be roughly linear, which means that strength and strain are proportional. Carbon fiber strands consist of several thousand fine-diameter (5–7 micron) single filaments as
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Company Grade
Carbon Ash assay content minimum, maximum, % %
Polycarbon, C-5 Inc. C-10 C-20
95
1
95 95
1 1
RK Carbon CA5 96 Fibers Grayon CA10 96 CA20 96
Breaking Density, Linear Yield, Filaments Twist, Plies Moisture Tensile Young’s strength g/cm3 density, m/kg per ply tpm nominal, strength, modulus, minimum, tex nominal % GPa GPa kg 9.3
1.4
310
3125
720
90
5
1
0.76
41
11 20
1.42 1.44
680 1280
1472 782
720 720
72 86
10 20
1 1
0.76 0.76
41 41
1
10
1.4
310
3225
720
90
5
0.75
0.82
34
1 1
13.6 25
1.4 1.4
630 1300
1587 769
720 720
80 75
10 20
0.75 0.75
0.82 0.82
34 34
Source: reprinted from manufacturer’s technical literature.
Technical textile yarns
Table 11.12 Properties of cellulose-based carbon fibers
Table 11.13 Properties of PAN-based carbon fibers Young’s Diameter, Elongation, Density, modulus, mm % g/cm3 GPa
Minimum carbon content, %
AKZO Fortafil Fibers Inc.
Fortafil 502,503,504,505 506,507,508,509 510,511,512,513 555,556
40 50 80 58
3.8 3.45 3.8 3.8
231 217 231 231
6 7 6 6.2
1.64 1.59 1.64 1.65
1.8 1.8 1.8 1.8
Afikim
Acif IS HT XHT HM
3,6,12,40,320 3,6,12,40 3,6,12 3,6,12
2.5 2.9 3.3 2.2
230 230 230 335
6.8 6.8 6.8 6.6
1.3 1.4 1.55 0.75
1.78 1.78 1.78 1.86
93 95 95 99.5
Cytec carbon fibers LLC
Thornel T300
1,3,6,12
3.75
231
7
1.4
1.76
92
T300C T650/35 T650/35C
3,6,12 3,6,12 12,24
3.75 4.28 4.28
231 255 248
7 6.8 6.8
1.4 1.7 1.7
1.76 1.77 1.77
92 94 94
Asahi Kasei
Hi-Carbolon
3,6,12
4.31
230
7
1.87
1.78
Grafil Inc. (Mitsubishi Rayon Co.)
Grafil 34-700 34-700WD 34-600, 34-600WD Pyrofil TR40 TR30S TR50S TRH50 MR35E MR40 MR50
12,24 12 48 1 3,6 12,24 12,24 12 12 12
4.5 4.5 4.15 4.7 4.41 4.9 4.9 4.41 4.41 5.4
234 234 234 235 235 240 255 295 295 290
7 7 7 7 7 7 7 7 6 6
1.9 1.9 1.9 2 1.9 2 1.9 1.5 1.5 1.8
1.8 1.8 1.8 1.8 1.79 1.82 1.8 1.75 1.76 1.8
349
Tensile strength, GPa
High modulus, high tenacity yarns
© Woodhead Publishing Limited, 2010
Company Fiber type Filament count, k
350
Table 11.13 Continued Tensile strength, GPa
Young’s Diameter, Elongation, Density, modulus, mm % g/cm–3 GPa
MS40 HR40 HS40
4.61 4.41 4.41
345 390 450
Hexcel
AS4 3,6,12 AS4C 3,6,12 AS4D 12 IM4 12 IMC 12 IM6 12 IM7 (5000 Spec) 6 IM7 (5000 Spec) 12 IM7 (6000 Spec) 12 IM7 (5000 Spec) 12 IM7C 12 IM8 12 IM9 6 IM9 12 IMC 12 PV36/700 12 PV42/800 12 PV42/850 12 UHM 3,6,12
4.48 4.04 4.69 4.8 5.52 5.59 5.18 5.52 5.76 5.76 5.52 5.59 6.07 6.14 5.52 4.69 5.52 5.76 3.45
231 7.1 1.87 1.78 231 6.9 1.88 1.78 245 6.7 1.92 1.79 276 6.7 1.74 1.78 290 1.9 1.8 279 5.2 2 1.76 276 5.2 1.87 1.78 276 5.2 2.01 1.78 290 5.1 1.99 1.79 292 2 1.8 290 5.4 1.9 1.8 304 5.1 1.84 1.79 290 4.4 2.1 290 4.4 2.1 1.8 290 5.4 1.9 1.8 248 1.9 290 5.4 1.9 1.8 292 4.4 1.97 441 0.8 1.87
IPCL
Indcarf 25 30
3,6,12 3,6,12
Min. 2.50 Min. 3.00
215–240 220–240
6.8 6.8
1.05–1.40 1.25–1.60
1.78 1.78
93 95
Kosco
Kosca GP250 HS300
12 12
2.8 3.3
220 230
6.8 6.8
1.3 1.4
1.8 1.8
93 95
12 12 12
6 6 5
1.3 1.1 1
Minimum carbon content, %
1.77 1.82 1.85 94
94 94 94 94 94 94 94 94 94 94
Technical textile yarns
© Woodhead Publishing Limited, 2010
Company Fiber type Filament count, k
Min. 2.0
180–240
8
1
1.75
>95
Min. 2.5
215–240
8
1.05–1.40
1.78
>95
Min. 3.0
220–240
7
1.25–1.60
1.78
>95
0.9–1.4 1.1–1.6
40–60 60–80
9–11 9–11
>1.9 >1.2
1.68–1.74 1.76–1.82
Toho Tenax Inc.
Tenax HTA HTS STS UTS IMS 3131 IMS 5131 HMA UMS 2526 UMS 3536
1,3,6,12,24 1,3,6,12,24 24 12,24 12 12,24 6,12 12,24 12
3.95 4.3 4 4.7 4.12 5.6 3 4.56 4.5
238 238 240 240 295 290 358 395 435
7 7 7 7 6.4 5 6.75 4.8 4.7
1.5 1.5 1.5 2 1.4 1.9 0.7 1.1 1.1
1.77 1.77 1.79 1.8 1.76 1.8 1.77 1.78 1.81
Textron
Avcarb HC HCB
2.07 1.9
207 262
1 0.72
Toho Tenax Inc.
Besfight HTA ST3 IM400 IM500 HM30 HM35 HM45 UM40
12 3,6,12 6,12 12 6,12 3,6,12 6,12 6,12
3.92 4.41 4.31 5 4.3 2.74 3.1 2.55
235 235 295 300 295 343 441 392
7 7 6.4 5 6.4 6.7 6.4 6.6
1.6 1.9 1.5 1.7 1.5 0.8 0.48 0.65
1.77 1.77 1.75 1.76 1.75 1.79 1.9 1.83
Toray
Torayca T300 T300J T400H
1,3,6,12 3,6,12 3,6
3.53 4.21 4.41
230 230 250
7 7 7
1.5 1.8 1.8
1.76 1.78 1.8
88–92 99.5
93 94 94
351
60,160,320, 400,410 60,160,320, 400,410 60,160,320, 400,410 320 320
High modulus, high tenacity yarns
© Woodhead Publishing Limited, 2010
SGL Sigrafil C10 C25 C30 T18 T16
352
Table 11.13 Continued Tensile strength, GPa
Young’s Diameter, Elongation, Density, modulus, mm % g/cm–3 GPa
T600S T700S T700G T800H T1000G M35J M40J M46J M50J M55J M60J M30S M40
24 12,24 12,24 6,12 12 6,12 6,12 6,12 6 6 3,6 18 1,3,6,12
4.31 4.9 4.9 5.49 6.37 4.7 4.41 4.21 4.12 4.02 3.82 5.49 2.74
230 230 7 240 294 5 294 5 343 6 377 5 436 5 475 5 540 5 588 4.7 294 6.5 392 6.5
1.9 2.1 2.1 1.9 2.2 1.4 1.2 1 0.8 0.8 0.7 1.9 0.7
1.79 1.8 1.8 1.81 1.8 1.75 1.77 1.84 1.88 1.91 1.94 1.73 1.81
Zoltek
Panex 33
48,160,320
3.8
228
1.6
1.81
Source: reprinted from manufacturer’s technical literature.
7.2
Minimum carbon content, % 93 96 99 99 99 99 99 99 98 99 94
Technical textile yarns
© Woodhead Publishing Limited, 2010
Company Fiber type Filament count, k
Table 11.14 Properties of pitch-based carbon fibers Young’s Diameter, Elongation, Density, modulus, mm % g/cm3 GPa
Minimum carbon content, %
Amoco
Thornel P25 P30X P55S P75S P100 P100S P100HTS P120 P120S K-800X K-1100
2,4 2 2,4 2 2 2 2 2 2 2 2
1.38 2.07 1.9 2.07 2.41 2.07 3.62 2.41 2.24 2.34 3.1
159 207 379 517 758 758 724 827 827 896 965
97 99 99 99 99 99 99
Ashland Oil Mitsubishi Kasei
Dialead K133 K135 K137 K139 K223 K321
4 2,4 4 2 4 2,4
2.35 2.55 2.65 2.75 2.84 1.96
441 539 637 735 10 225 10 176
0.53 0.47 0.42 0.37 1.21 1.08
2.08 2.1 2.12 2.14 2 1.9
Nippon Graphite Fiber Corp.
Granoc XN50A XN70A XN80A XN85A YS50A YS70A YS90A YS50 YS60
0.5,2 0.5,1,2 1,2 1,2 4.5 4.5 3 3,4.5 3,4.5
3.83 3.63 3.63 3.63 3.83 3.63 3.63 3.73 3.53
520 720 785 830 520 720 880 490 590
0.7 0.5 0.5 0.4 0.7 0.5 0.4 0.8 0.6
2.14 2.16 2.17 2.17 2.14 2.16 2.19 2.09 2.12
11 0.9 11 10 0.5 10 0.4 10 0.32 10 0.27 10 0.5 10 0.29 10 0.29 10 10
10 10 10 8.5 7 7 7 7 7
1.9 2 2 2 2.16 2.16 2.17 2.17 2.17 2.2 2.2
353
Tensile strength, GPa
High modulus, high tenacity yarns
© Woodhead Publishing Limited, 2010
Company Fiber type Filament count, k
354
Table 11.14 Continued Tensile strength, GPa
Young’s Diameter, Elongation, Density, modulus, mm % g/cm3 GPa
YS70 YS80 YT-50-10S
3,4.5 3,4.5 1
3.53 3.53 4.05
690 785 490
7 7 6
Osaka Gas Petoca
Donacarbo Carbonic HM50 HM60 HM70
2 2 2 1,2
3 2.75 2.94 2.94
500 490 588 686
9 10 10 10
0.6 0.56 0.5 0.43
2.1 2.16 2.17 2.18
Tonen Corp.
Forca FT500 FT700
3 3
3 3.3
500 700
10 10
0.6 0.5
2.14 2.16
Source: reprinted from manufacturer’s technical literature.
0.5 2.14 0.5 2.15 0.8
Minimum carbon content, %
Technical textile yarns
© Woodhead Publishing Limited, 2010
Company Fiber type Filament count, k
High modulus, high tenacity yarns 7
Cellulose based PAN based
6
Strength (GPa)
355
Pitch based
5 4 3 2 1 0
100 200 300 400 500 600 700 800 900 1000 Modulus (GPa)
11.7 Tensile properties of carbon fibers.
shown in Tables 11.12–11.14; therefore, when they are subjected to tensile load, failure is likely to initiate in a local region of a single filament because of the influence of the local value of the filament and the geometry of that region. Hence it is not practical to discuss the tensile strength of the carbon fibers themselves. As most carbon fibers are used in a composite form (as carbon fiber reinforced plastics), nowadays the tensile strength of carbon fiber is determined by the impregnated strand method (JIS-R-7601) [14], which is a kind of composite tensile strength. Several test methods such as tensile recoil [15], unidirectional composite, broken fiber fragment length, loop, and fiber encapsulated into block tests have been used for determining the compressive strength of carbon fibers [16]. Compressive strengths for various types of carbon fibers are shown in Table 11.15. These compressive strength values were determined from the compressive strength of composites by normalizing to 100% fiber [17]. The compressive behaviors are rather different from those of the tensile properties. When compressive load is applied in parallel with the fiber axis, fiber microstructure disintegration occurs at the break. Electrical properties The electrical resistance of the carbon fibers Torayca, Besfight and Amoco decreases with increasing Young’s modulus. These values are shown in Table 11.16. Matsubara et al. [18] have measured electrical resistivity and thermoelectric power at temperatures from 0 to 300 K for Torayca
© Woodhead Publishing Limited, 2010
356
Technical textile yarns
Table 11.15 Compressive properties of carbon fibers Company Commercial Young’s Tensile name modulus, strength GPa (st), GPa
Compressive strength sc/st (sc), GPa
Density, g/cm3
Amoco Thornel T-300 T-40 T-50
2.88 2.76 1.61
1.79 1.78 1.81
231 290 393
3.24 5.60 2.41
0.9 0.48 0.67
BASF Celion
GY-7
517
1.86
1.06
0.59
1.96
Hercules Magnamite
AS-4
231
3.64
2.69
0.75
1.80
IM8
310
5.17
3.22
0.62
1.8
Toray Torayca
T-1000 M40J M60J
295 390 590
7.1 4.40 3.8
2.76 2.33 1.67
0.39 0.53 0.44
1.82 1.77 1.94
Source: Ref. 17 with kind permission of Springer Science + Business Media.
intermediate (TH series) (T800H, T-1000G) and HM (MJ series) type (M40J, M46J, M50J, M60J) fibers. According to their results, the M-type (J-series) fibers indicate the semiconductor-like temperature dependence all over the temperature ranges examined, and the resistivity increases with decreasing elastic modulus. On the contrary, the T-type fibers exhibit a peak in resistivity around 35 K. The metallic-like temperature dependence observed in spite of their lower crystallite perfection compared with M-type fibers can be explained by considering the Rayleigh wave phonon whose velocity is so small that a number of phonons are excited even at liquid helium temperature. They explained the behavior assuming a mixture model of the band conduction and two-dimensional variable-range hopping conduction. Thermal properties Early work showed that the thermo-oxidative instability of carbon fibers affected the stability of high temperature laminates at 300°C. Carbon fibers oxidize in air and Fig. 11.8 shows the weight loss of Grayon fibers made from a viscose rayon precursor, where the more graphitic version has the best oxidation resistance. The thermal stability of oxidized PAN and PAN-based carbon fibers is compared with that of an aramid in Fig. 11.9. The thermal oxidative behavior in air of several grades of PAN-based carbon fibers was studied by Gourdin [19] and the weight losses at 250°C as a function of time in air are shown in Fig. 11.10. This shows that fibers produced at the highest production temperatures, such as HTS and HMS, did have the best thermo-oxidative resistance. The coefficient of longitudinal thermal expansion of carbon fibers decreases with increasing Young’s modulus. This can be observed in Table 11.16 where
© Woodhead Publishing Limited, 2010
High modulus, high tenacity yarns
357
Table 11.16 Functional properties of selected types of carbon fibers Company Fiber type
Carbon Young’s Electrical Specific CTE, Thermal content, modulus, resistivity, heat, ¥ 10–6/°C conductivity, % GPa 10–3 W cm cal/g°C cal/cm s°C
Amoco (Thornel)
T-300 92 T-40 94 T650/42 94 T-50 99 P-25 P-30X P-55S 97 P-75S 99 P-100S 99 P-120S 99 K-1100 99
231 290 290 390 159 207 379 517 758 827 965
1.8 1.45 1.42 0.95 1.30 1.12 0.85 0.7 0.25 0.22 0.13
Tenax
HTA IMS
238 290
1.6 0.17 1.45
Toho rayon (Besfight)
HTA IM400 HM35 HM40
235 295 345 380
1.5 1.4 1 0.9
230 230 250 230 294 294 343 377 436 475 540 588
1.7 1.5 1.6 1.6 1.4 1.4 1.1 1.0 0.9 0.9 0.8 0.7
Toray T300 (Torayca) T300J T400H T700S T800H T1000G M35J M40J M46J M50J M55J M60J
93 94 94 93 96 95 >99 >99 >99 >99 >99 >99
0.17 –0.6 0.17 –0.75 0.17 –0.75 0.17 –1.13 0.17 0.17 0.17 –1.30 0.17 –1.46 0.17 –1.48 0.17 –1.50 0.17 –1.50
0.19 0.18 0.18 0.18 0.18 0.18 0.17 0.17 0.17 0.17 0.17 0.17
–0.1
–0.41 –0.43 –0.45 –0.38 –0.56 –0.55 –0.73 –0.83 –0.9 –1.0 –1.1 –1.1
4.1 ¥ 10–2
2.5 ¥ 10–2 2.23 ¥ 10–2 2.52 ¥ 10–2 2.24 ¥ 10–2 8.39 ¥ 10–2 7.65 ¥ 10–2 9.33 ¥ 10–2 1.64 ¥ 10–1 2.02 ¥ 10–1 2.34 ¥ 10–1 3.72 ¥ 10–1 3.63 ¥ 10–1
Source: reprinted from manufacturer’s technical literature.
the coefficient of thermal expansion (CTE) values for Torayca and Thornel fibers increase with Young’s modulus. The thermal conductivity of carbon fibers increases with increasing Young’s modulus. This also can be seen in Table 11.16.
11.3.3 Applications There are many types of carbon fibers from many manufacturers, which are suited to different applications including aerospace, sporting goods, and a variety of commercial/industrial applications. Some of their applications for these fields are listed in Table 11.17. Developments occur very rapidly
© Woodhead Publishing Limited, 2010
Technical textile yarns Grayon graphitized
0 10 Grayon carbonized
Weight loss, %
20 30 40 50 60 70 80 90 100
100
200
300 400 500 600 Air temperature, °C
700
800
11.8 Grayon (carbonized rayon) carbon fiber weight loss vs temperature in air (reprinted from RK Carbon Fiber’s technical literature).
100 Sigrafil C® carbon fiber
90 Weight loss of specimen, %
358
Panox
80
®
70 60 50 40
Heating rate 10°C/min Weight of specimen 30 mg Air flow 120 liter/min
30 Aramid
20 10 0 200
300
400 500 Temperature, °C
600
700
11.9 Thermal stability of oxidized PAN and PAN-based carbon fibers (reprinted from SGL Carbon Group’s technical literature).
© Woodhead Publishing Limited, 2010
High modulus, high tenacity yarns T300B 6000 T300B 3000 E xas t300c 6000 Celion epoxy celion polyimide HMS HTS-2 AS-4
30
Weight loss, %
359
20
10
0
1000
2000 3000 Time, hours
4000
5000
11.10 Weight loss of carbon fibers after aging at 250°C (reprinted from Ref. 19). Table 11.17 Applications of carbon fibers and yarns Field
Applications
Aerospace Sports Industrial
Aircraft, rockets, satellites Fishing equipment, golf clubs, rackets, marine, others Automobiles, motorcycles, bicycles, cars and containers, machinery parts, high-speed rotors, electric/electronic parts, pressure vessels, chemical equipment, medical equipment, construction, office equipment, precision equipment, corrosion resistant equipment, others
Source: authors’ summary.
in the composites field and some of these applications may now have been discontinued or replaced, but they serve to illustrate the diverse applications of carbon fibers.
11.3.4 Future trends Most of the effort expended on carbon fibers is directed at the following aspects: cost reduction, manufacturing process, property standardization, recycling, and innovative developments. Carbon fibers are too expensive to use in many fields. Prospects for cost reduction can stimulate interest in many new applications. Manufacturing process improvements include increasing the speed of production and reducing the filament diameter. Property standardization is an important trend. Glass fiber is easy for a designer to design with according to end-
© Woodhead Publishing Limited, 2010
360
Technical textile yarns
use because the fibers are supplied in standard form by suppliers. Carbon fiber suppliers have many grades to choose from, with little commonality among producers. Another important aspect of the composite world is the issue of recycling. Recycling of carbon fiber products will be a hot topic in the future. Carbon fibers also need innovative developments. Certainly, the future of carbon fibers may be strongly influenced by nanotechnology, such as carbon nanofibers, nanoporous carbon fibers and carbon nanotubes.
11.4
Ceramic fibers and yarns
Ceramic fibers are those continuous fibers made of ceramic materials which are resistant to high temperatures (2000–3000°F). Continuous ceramic fibers are commercially available in two general classes: (1) non-oxide fibers, based primarily on b-phase silicon carbide (SiC); and (2) oxide fibers, based on the alumina–silica (Al2O3–SiO2) system and on a-alumina (a-Al2O3). The production of fine ceramic fibers first requires an organic or mineral precursor fiber, which is then heat-treated and pyrolyzed for a very short time. Ceramic fibers can be produced by chemical vapor deposition, melt drawing, spinning and extrusion.
11.4.1 Compositions, structures and properties Non-oxide fibers (SiC-based) Silicon carbide-based (SiC) fibers have high stiffness and good mechanical properties at high temperature in air. The properties and compositions of currently commercially available SiC-based fibers are listed in Table 11.18. The fibers range from first-generation fibers with very high percentages of oxygen and excess carbon, such as Nicalon and Tyranno Lox-M, to the more recent near-stoichiometric (atomic C/Si ≈ 1) fibers, such as Tyranno SA [20] and Sylramic [21]. The first fine SiC-based fibers were reported by Yajima et al. [22] and commercialized under the name of Nicalon fibers by Nippon Carbide Inc. and that of Tyranno fibers by Ube Industries at the beginning of the 1980s. These fibers are produced by the conversion of polycarbosilane (PCS) and polytitanocarbosilane (PTC) precursor fibers which contain cycles of six atoms arranged in a similar manner to the diamond structure of b-SiC, respectively. The Nicalon NL-200 fibers, which are the most representative of this class of ceramic fibers, have a diameter of 14 mm, a glassy appearance, and a Young’s modulus of 190 GPa. PTC precursor, which was obtained by the grafting of titanium alkoxide between the PCS chains [23], was reported to be more easily spinnable. A series of fibers from a PTC was produced by Ube Industries. For example, Tyranno LOX-M fibers, with diameters
© Woodhead Publishing Limited, 2010
Table 11.18 Properties and compositions of silicon-based fibers Young’s modulus, GPa
Si-C based Nippon Carbide Nippon Carbide Ube Industries Ube Industries
Nicalon 56.6% Si, 31.7% C, 11.7% O NL-200 Hi-Nicalon 62.4% Si, 37.1% C, 0.5% O Tyranno Lox-M Tyranno Lox-E
54.0% Si, 31.6% C, 12.4% O, 2.0% Ti 54.8% Si, 37.5% C, 5.8% O, 1.9% Ti
Near- Nippon Hi-Nicalon, stoichiometric Carbide Type-S 68.9% Si, 30.9% C, 0.2% Ti SiC Ube Industries Tyranno SA1 SiC, Al < 1%, + small amounts of C+O Ube Industries Tyranno SA3 Dow Corning Sylramic SiC ~96%, TiO2 ~3.0%, C ~1.0%, O ~0.3% Source: reprinted from manufacturer’s technical literature.
14
2.55
2
1.05
190
14
2.74
2.6
1
263
2.37
2.5
1.4
180
11
2.39
2.9
1.45
199
13
3
2.5
0.65
375
10
3
2.6
0.75
330
7.5 10
3.1 3.1
2.9 3
0.8 0.75
340 390
8.5
High modulus, high tenacity yarns
© Woodhead Publishing Limited, 2010
Fiber type Company Trade mark Composition, wt% Diameter, Density, Strength, Strain to mm g/cm3 GPa failure, %
361
362
Technical textile yarns
down to 8.5 mm and containing 13% oxygen by weight, were produced after oxidation, curing and pyrolysis at around 1300°C. These two types of fibers show much inferior creep properties above 1000°C. Creep is due to the presence of the oxygen-rich intergranular phase. The further improvement of SiC-based fibers required the elimination of oxygen from the structure. This was achieved by Nippon Carbide Inc. by crosslinking the PCS precursors using electron irradiation so avoiding the introduction of oxygen. The fibers, which were pyrolyzed up to about 1400°C and contained 0.5 wt% oxygen, are known as Hi-Nicalon fibers [24]. The radiation curing process was also used by Ube Industries to crosslink PTC fibers. After a pyrolysis at around 1300°C, the LOX-E fiber that was obtained contained 5 wt% of oxygen. This higher value of oxygen in the LOX-E fiber compared to that of the Hi-Nicalon was due to the introduction of titanium alkoxides for the fabrication of the PTC. The decrease in oxygen content in the Hi-Nicalon and LOX-E compared with NL-200 and LOX-M has resulted in an increase in the strength and modulus. Near-stoichiometric SiC fibers from polymer precursors are produced by the above two producers and by Dow Corning by the use of higher pyrolysis temperatures. This leads to larger grain sizes and the development of a sintered material. Nippon Carbide Inc. has obtained a near-stoichiometric fiber, the Hi-Nicalon Type-S [25], from a polycarbosilane precursor cured by electron irradiation and pyrolyzed by a modified Hi-Nicalon process in a closely controlled atmosphere above 1500°C. As a result, the C/Si ratio is reduced from 1.39 for the Hi-Nicalon to 1.05 for the Hi-Nicalon Type-S as shown in Table 11.18. Ube Industries has developed a near-stoichiometric fiber named Tyranno SA made from polyaluminocarbosilane precursor. The precursor fiber is cured by oxidation at first, and then pyrolyzed to 1300°C to form an oxygen-rich SiC fiber, thereafter up to 1800°C to allow the outgassing of CO between 1500 and 1700°C, ending with sintering. Less than 1 wt% of Al has been added as a sintering aid and the manufacturer claims that it gives better corrosion resistance compared with other metals. Dow Corning has produced stoichiometric SiC fibers using PTC precursors containing a small amount of titanium. These fibers are cured by oxidation and doped with boron, which acts as a sintering aid. The precursor fiber is pyrolyzed at around 1600°C to form a near-stoichiometric fiber called Sylramic fiber. Comparing these three types of near-stoichiometric fibers with the other fibers, it can be seen that the strength and modulus are both increased and with much improved creep properties. Oxide fibers Oxide fibers find uses both as insulation and as reinforcements for their refractory properties. Commercial oxide fibers can be divided into three
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High modulus, high tenacity yarns
363
compositional chasses: (1) pure alumina fibers consisting primarily of a-Al2O3; (2) alumina–silica fibers, that is, those consisting of a mixture of transition alumina and amorphous silica; and (3) a-alumina–zirconia fibers consisting of a mixture of b-Al2O3 and ZrO2. The properties and compositions of these fibers are listed in Table 11.19. Pure alumina fibers are the most stable because they contain crystalline a-Al2O3. They are more resistant to shrinkage at high temperatures caused by crystallization and sintering and can have higher creep resistance. The FP fiber, manufactured by DuPont in 1979 [26], was the first wholly a-alumina fiber to be produced. It was continuous with a diameter of around 20 mm. This fiber was composed of 99.9% a-alumina and had a density of 3.92 g/cm3, a polycrystalline microstructure with a grain size of 0.5 mm and a high Young’s modulus (410 GPa), but its low strength (1.2 GPa) and strain to failure (0.29%) made the fiber unsuitable for weaving [27,28]. FP fibers are chemically stable in air at high temperature. However, they are prone to grain sliding and creep due to their isotropic fine-grained microstructures. Reduction of diameter can improve the flexibility and hence the weavability of the fibers, and flexible a-alumina fibers require diameters of around 10 mm. This was first achieved by Mitsui Mining by reducing the size of the a-alumina powder, resulting in Almax [29]. Later, a continuous a-alumina fiber with the trade name of Nextel 610 fiber and a diameter of 10 mm was produced by 3M [30]. It is composed of around 99% a-alumina and includes 0.4–0.7% Fe2O3 used as a nucleating agent and 0.2–0.3% SiO2 as a grain growth inhibitor. Nextel 610 possesses the highest strength of the three a-alumina fibers described, as shown in Table 11.19. Alumina–silica fibers were the first ceramic fibers, produced in the early 1970s for thermal insulation applications. Saffil fiber is a discontinuous fiber of the alumina–silica type with a diameter of 3 mm and was introduced by ICI in 1972 [31]. It consists of a-alumina and 4% silica. Continuous Altex fiber is produced by Sumitomo Chemicals. The fiber consists of small g-alumina grains of a few tens of nanometers intimately dispersed in an amorphous silica phase [32]. The 3M Corporation produces a range of ceramic fibers having the composition of mullite under the general name of Nextel. Nextel 312 fiber first appeared in 1974 and is composed of 62 wt% Al2O3, 24 wt% SiO2 and 14 wt% B2O3. The addition of B2O3 lowered the temperature of mullite formation, helped sintering and increased the fiber strength. To improve the high-temperature stability in the more recent Nextel 440 fiber, the amount of B2O3 has been reduced. The dispersion of small particles of tetragonal zirconia between a-alumina grains could improve the flexibility of oxide ceramic fibers. A flexible a-alumina–zirconia fiber, Nextel 650, has been introduced by 3M; it has a higher creep resistance than the a-alumina Nextel 610 fiber. The effect of the addition of zirconia on the high-temperature mechanical behavior is to
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© Woodhead Publishing Limited, 2010
Fiber type Manufacturer Trade mark Composition, wt% Diameter, Density, Strength, Strain to mm g/cm3 GPa failure, %
Young’s modulus, GPa
a-Al2O3 fibers Du Pont FP Mitsui Mining Almax 3M Nextel 610
99.9% Al2O3 99.9% Al2O3 99% Al2O3, 0.2–0.3% SiO2, 0.4–0.7% Fe2O3
Alumina–silica ICI Saffil fibers Sumitomo Altex 3M Nextel 312 3M Nextel 440 3M Nextel 720
95% Al2O3, 85% Al2O3, 62% Al2O3, 14% B2O3 70% Al2O3, 2% B2O3 85% Al2O3,
Alumina– 3M Nextel 650 zirconia fibers
89% Al2O3, 10% ZrO2, 1% Y2O3
Source: reprinted from manufacturer’s technical literature.
20 10 10–12
3.92 3.6 3.75
1.2 1.02 1.9
0.29 0.3 0.5
414 344 370
5% SiO2 1–5 3.2 15% SiO2 15 3.2 24% SiO2, 10–12 or 8–9 2.7
2 1.8 1.7
0.67 0.8 1.12
300 210 152
28% SiO2,
10–12
3.05
2.1
1.11
190
15% SiO2
12
3.4
2.1
0.81
260
11
4.1
2.5
0.7
360
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Table 11.19 Properties and compositions of alumina-based fibers
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365
delay the onset of plasticity to 1100°C and to decrease the strain rates in creep.
11.4.2 Commercial products of ceramic yarns Ceramic fibers are supplied as multi-filament tow, the standards being listed in Table 11.20. They are also supplied in other yarn forms such as twist yarn and rope, though these forms of products are not standardized.
11.4.3 Applications Due to their ability to withstand high temperatures, ceramic fibers can be used in numerous applications, including tube seals, thermocouples, horse-tail curtains, furnace curtains, heat shields, ladle covers, resistance wire supports, conveyor belts, expansion joints, furnace linings, delay table covers, zone dividers, seals and gaskets.
11.4.4 Future trends SiC fibers are the preferred reinforcement for ceramic-matrix composites (CMC) due to their low atomic diffusion and high thermal conductivity. The reduction in production costs and improvement in high-temperature thermal conductivity and fracture life are high-priority development issues for future SiC-based fibers. Although the creep resistance of oxide fibers is inferior to that of SiCbased fibers, recently developed oxide fibers have demonstrated adequate creep resistance for use in structural composites up to 1100°C (2000°F). Further increases in temperature capability are possible. Another interesting area for research is the development of fine-grained, fully crystalline fibers of creep-resistant multi-component oxides such as mullite and zirconia. The advantages of environmental stability and low cost will continue to provide incentives for further improvements in the high-temperature properties of oxide fibers.
11.5
Basalt fibers and yarns
11.5.1 Composition and structure Basalt fibers are made from extremely fine fibers of basalt which is composed of the minerals plagioclase, pyroxene, and olivine. The compositions of basalt fibers are shown in Table 11.21. Basalt fibers are produced in a continuous process similar in many respects to that used to make glass fibers. The manufacture of basalt fiber requires the melting of the quarried basalt rock
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Trade name Nicalon Hi-Nicalon Tyranno Hi-Nicalon, Tyranno Sylramic Almax Nextel Altex NL-200 Lox-M, Type-S SA1,3 610 Lox-E
Nextel Nextel 312, 440, 650 720
Filaments 500 500 400/800 500 800/1600 800 1000 per tow
420/780
Source: reprinted from manufacturer’s technical literature.
420/780/2600
500/1000
780
Technical textile yarns
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Table 11.20 Standards for ceramic rovings
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Table 11.21 Composition ranges for commercial basalt fibers Chemical components
Percentage by mass
SiO2 Al2O3 CaO MgO Na2O + K2O TiO2 Fe2O3 + FeO Others
51.6–59.3 14.6–18.3 5.9–9.4 3.0–5.3 3.6–5.2 0.8–2.25 9.0–14.0 0.09–0.13
Source: reprinted from manufacturer’s technical literature.
at about 1400°C (2500°F). The molten rock is then extruded through small nozzles to produce continuous filaments of basalt fiber. Here, the process is actually simpler than glass fiber processing because the basalt fiber has a less complex composition. There are three main manufacturing techniques: centrifugal-blowing, centrifugal-multiroll and die-blowing. The fibers typically have a filament diameter of between 9 and 13 mm which is far enough above the respiratory limit of 5 mm to make basalt fiber a suitable replacement for asbestos. They also have a high elastic modulus, resulting in excellent specific tenacity.
11.5.2 Properties Basalt is an inert and naturally occurring material that is found worldwide. Basalt-based materials are environmentally-friendly and not hazardous. Basalt continuous fibers are produced from basalt rock using single-component raw material by drawing and winding fibers from the melt. The main features of basalt fibers include high strength and high modulus with excellent shock resistance; they are a low-cost alternative and can replace carbon fiber in some applications. Physical properties The physical properties of basalt fiber compared with other inorganic fibers are listed in Table 11.22. It can be seen that basalt fibers have better mechanical properties than glass fibers, and a little worse than carbon fibers. However, the maximum service temperature of basalt fiber is the highest. Chemical resistance Basalt fibers also have high chemical durability against the impact of water, salts, alkalis and acids. Unlike metal, basalt is not affected by corrosion.
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Table 11.22 Comparative physical properties between basalt fiber and other inorganic fibers Capability
CBF
E-glass fiber S-glass fiber
Carbon fiber
Density, g/cm3 Tensile strength, MPa Elastic modulus, GPa Elongation at break, % Diameter of filament, µm Linear density, tex Temperature of application, °C
2.63–2.8 3000–4840 79.3–93.1 3.1 6–21 60–4200 –260–+650
2.54–2.57 3100–3800 72.5–75.5 4.7 6–21 40–4200 –60–+460
1.78 3500–6000 230–600 1.5–2.0 5–15 60–2400 –50–+500
2.54 4020–4650 83–86 5.3 6–21 40–4200 –50–+300
Source: reprinted from manufacturer’s technical literature. Table 11.23 Chemical durability of basalt fibers (weight after 3 hours boiled (%)) Diameter of elementary fibers, µm
H2O
0.5 H NaOH
2 H NaOH 2 H HCl
17 12 9
99.63 99.7 99.6
98.3 98.9 94.6
92.8 90.7 83.3
76.9 49.9 38.8
Source: reprinted from manufacturer’s technical literature.
Unlike fiberglass, basalt fiber is not affected by acids. Basalt fibers possess high corrosion and chemical durability qualities towards corrosive media such as salts, acid and alkali solutions, as shown in Table 11.23.
11.5.3 Commercial products of basalt yarns To date, basalt fibers are being used commercially in the form of roving, continuous filament yarns and textured yarns. These products are made in various sizes to meet industrial requirements. Rovings Continuous basalt roving is made of a bundle of parallel strands without twisting. Some of the technical data extracted from manufacturers’ data sheets are listed in Table 11.24. Continuous basalt roving can be used in many fields such as filament-winding of various pipes, tanks and cylinders, various woven rovings, mesh fabrics and geotextiles, repair (healing) and strengthening of infrastructures. For example, continuous basalt rovings of 1200 tex and 2400 tex are preferred for making mesh fabrics, geogrids and base cloth for high-temperature filtration needled felts, which can be reliably used over a wide range of temperatures from –260°C to 650°C.
© Woodhead Publishing Limited, 2010
Company Product Diameter, mm
Linear SD Sizing density, tex
Sizing Moisture, Tensile content, % strength, % GPa
LBIE
CBF7-400 7 400 CBF9-800 9 800 CBF13-800 13 800 CBF13-1200 13 1200
±20 ±40 ±40 ±60
Silane Silane Silane Silane
£ £ £ £
Kamenny Vek
KV11 KV11 KV12 KV12
±5% ±5% ±5% ±5%
Silane Silane Silane Silane
≥ 0.5 ≥ 0.5 ≥ 0.5 ≥ 0.5
Assembled TDS Direct TDS Assembled TDS Direct TDS
10–20 270–4800 10–20 68–350 10–20 270–4800 10–20 68–350
Source: reprinted from manufacturer’s technical literature.
0.04 0.04 0.04 0.04
Young’s modulus, GPa
<0.01 <0.01 <0.01 <0.01 <0.1 <0.1 <0.1 <0.1
3.0–3.2 2.9–3.2 3.0–3.2 2.9–3.2
85–90 84–94 85–90 84–94
High modulus, high tenacity yarns
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Table 11.24 Technical data of basalt rovings
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Technical textile yarns
Continuous filament yarns Continuous basalt filament yarns are made of multiple basalt strands by primary twisting (usually the filament diameter is under 9 mm) and can be divided into weaving yarns and industrial yarns. Weaving yarns are usually made into cylindrical or milk bottle-shaped packages. The technical data of continuous filament yarns are listed in Table 11.25. These yarns can be used in fabrics and tapes resistant to acids, alkalis and high temperature, base cloths of needled felt, base cloths for electrical insulation boards, electrical insulation yarns and threads, advanced heat-resistant and chemical-resistant fabrics, unidirectional fabrics with high temperature resistance, high elastic modulus, high strength, etc. Textured yarns With a high-performance bulked yarn machine, basalt fiber also can be fabricated into textured yarns. The technical data of textured yarns are listed in Table 11.26. Fabrics made from such textured yarn are softer and have good handle touch, and they are suitable for manufacturing high-temperature filters. Their good appearance makes them suitable for manufacturing fire curtains.
11.5.4 Applications Due to their high service temperature and high performance, basalt fiber products can be used in various fields, such as machinery and automobile construction, shipbuilding, carriage building, aviation, rocket production, power generation, atomic engineering, the electronic, chemical and petrochemical industries, metallurgy, cryogenic technologies and equipment, building materials, fireproof materials, port construction, sea platforms, ceramics and porcelain, agriculture, municipal services and home appliances.
11.5.5 Future trends Though basalt itself is an environmentally friendly natural material, the consumption of energy in producing basalt fibers is too high. This may add to the greenhouse effect and waste energy resources. Energy saving is a very important issue for the future development of basalt fibers.
11.6
Aramid fibers and yarns
11.6.1 Composition and structure Aramid fibers are a class of high heat-resistant synthetic fibers with high mechanical performance. They belong to aromatic polyamides which were
© Woodhead Publishing Limited, 2010
Company Product
Diameter, Linear mm density, tex
Tolerance, Twist/m tex
Sizing type
±2% 68 ± 5 ±2% 120 ± 5 ±2% 68 ± 5
texfile texfile texfile
LBIE
CBF7-22 ¥ 2-S68 7 CBF6-12 ¥ 4-S120 6 CBF9-33 ¥ 2-S68 9
Kamenny Vek
TDS BTY 9–13 20–150 BTY10-68-KV12 10 ± 0.5 68 ±5% 20–150 BTY10-68 ¥ 2-KV12 10 ± 0.5 136 ±5% 20–150
45 48 66
Source: reprinted from manufacturer’s technical literature.
Silane Silane Silane
Sizing Moisture, content, % %
≥ 0.4 ≥ 0.4 ≥ 0.4
< 0.5 < 0.5 < 0.5
Tensile strength, mN/tex
550–700 > 700 > 700
High modulus, high tenacity yarns
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Table 11.25 Technical data of basalt continuous filament yarns
371
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Technical textile yarns
Table 11.26 Technical data of basalt textured yarns Company Product Diameter, mm Linear density, tex
Sizing
Moisture, %
LBIE
Special Special Special Special
£ £ £ £
BT13-800 BT13-1200 BT9-400 BT9-260
13 13 9 9
800 1200 400 260
± ± ± ±
40 60 60 20
0.1 0.1 0.1 0.1
Source: reprinted from manufacturer’s technical literature.
N
N
H
H
O
O
C
C n
11.11 The meta-aramid Nomex® aramid fiber.
N
N
H
H
O
O
C
C n
11.12 The para-aramid Kevlar® aramid fiber.
NH
NHOC
CO
HN
O
m
NHOC
CO n
11.13 The Technora® aramid copolymer fiber.
first introduced in commercial applications in the early 1960s, with a metaaramid fiber produced by DuPont under the trade name Nomex® (Fig. 11.11). A much higher-tenacity and higher-modulus fiber with para-aramid was developed and commercialized also by DuPont, under the trade name Kevlar® in 1971 (Fig. 11.12). Another para-aramid, Twaron® (Twaron® is a registered product of Teijin), similar to Kevlar®, and an aramid copolymer fiber Technora® (Fig. 11.13) (Technora® is a registered product of Teijin) [33], appeared on the market towards the end of the 1980s. The chemical formulas of these fibers are presented in Figs 11.11–11.13. A schematic representation of the microstructure of a semicrystalline polymer such as nylon 6 and para-aramid is outlined in Fig. 11.14. As the
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(a)
373
(b)
11.14 Schematic representation of the microstructure of (a) semicrystalline polymers such as nylon 6 and (b) para-aramid (reproduced from Ref. 34).
chain molecules of aramid fibers are highly oriented along the fiber axis, the strength of the chemical bond can be exploited [34].
11.6.2 Properties The main properties of aramid fibers include good resistance to abrasion, good resistance to organic solvents, non-conductivity, no melting point, degradation starting from 500°C, low flammability, good fabric integrity at elevated temperatures, sensitivity to acids and salts, sensitivity to ultraviolet radiation, and proneness to static build-up unless finished. Physical properties The physical properties of some commercially available aramid filaments are listed in Table 11.27. It can be seen that the modulus and tensile strength increase from Kevlar® 29 to Kevlar® 149. However, the tensile strength of meta-aramid fibers and aramid copolymer fibers is lower than that of para-aramid. Although the tensile strength and modulus of aramid fibers are significantly higher than those of earlier organic fibers, their elongation is lower. For instance, the as-spun Kevlar® aramid fiber exhibits over twice the tenacity and nine times the modulus of high-strength nylon [35]. On a weight basis it is stronger than steel wire and stiffer than glass. The latter properties resemble those of inorganic fibers and, of course, can be attributed to the extended chain morphology, high molar mass and excellent orientation in a thermally stable structure that does not melt. Para-aramid fibers have utility due to a combination of superior properties allied with features usually
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Type
Specific gravity g/cm3
Filament diameter, mm
Kevlar® 29 1.44 12 Kevlar® 49 1.44 12 Kevlar® 149 1.47 12 Nomex® 1.46 Twaron® Twaron® High Modulus Technora® 1.39 Source: reprinted from manufacturer’s technical literature.
Tensile strength, MPa
Young’s Strain to Moisture modulus, failure, % regain, % GPa
Thermal decomposition temperature, °C
2920 3000 3400 46 195 195 204
70.5 112.4 179 13 104 130 87
427–482 427–482 415
3.6 4.5 2.4 3.5 1.3 35 3.6 2.5 4.4 2
500
Technical textile yarns
© Woodhead Publishing Limited, 2010
Table 11.27 Physical properties of aramid types
High modulus, high tenacity yarns
375
associated with organic fibers such as low density, easy processability and rather good fatigue and abrasion resistance. Therefore, these materials are a suitable replacement for metal. Chemical resistance Nomex® has good resistance to many chemicals. Its acid resistance is much better than that of Nylon 6,6, but not as good as that of polyester or polyacrylic fibers. It exhibits good resistance to alkali at room temperature, but is degraded by strong alkali at elevated temperatures. Most organic solvents have little effect and most aqueous salt solutions have no effect at all on the breaking strength of Kevlar® fiber. However, strong acids and bases do attack para-aramid at elevated temperatures or high concentrations. Kevlar® is also susceptible to hydrolysis under certain conditions [36]. Hydrolytic polymer degradation leads directly to the strength loss of Kevlar® fiber. Morgan et al. [36] concluded that the strength loss of Kevlar® fiber in typical environmental conditions is not a serious problem. The catalytic activities of salts in Kevlar® fiber are also believed to be limited. Technora® fiber exhibits good chemical resistance to a number of common acids, alkalis, and solvents. It is also hydrolytically stable in seawater and steam. The strong chemical resistance of Technora® fiber is not well understood, but may be associated with its highly drawn fiber morphology. Thermal properties Nomex® is a heat- and flame-resistant fiber which has a specific heat of 0.29 cal/g°C and will degrade rapidly at temperatures above 371°C. It has a thermal conductivity of 0.9 BTU/h ft °F for 1 inch thickness. Meta-aramid fiber has a linear coefficient of expansion of 1.12 ¥ 10–5 in/in°F between 21 and 204°C after heat setting at 280°C [37]. Kevlar® does not melt and decomposes at relatively high temperatures (427–482°C) in air and at approximately 538°C in nitrogen. Increasing temperatures reduce the modulus, tensile strength and break elongation of Kevlar® fiber. This should be taken into consideration when using Kevlar® at or above 149–177°C for extended periods of time. Technora® fiber decomposes at 500°C and the ignition point of Technora® is about 650°C. Its heat of combustion is 6800 cal/g. The specific heat of Technora® is 0.26 cal/g°C.
11.6.3 Commercial products of aramid yarns The major aramid fiber forms continuous filament yarns, spun yarns and textured yarns.
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Technical textile yarns
Continuous filament yarns Different available yarn sizes of Kevlar® 49 and 29 are listed in Table 11.28. They are multifilament products directly spun during fiber manufacture and range from a very fine, 25-filament yarn to 1333-filament yarns. Kevlar® 29 yarns, which have a lower tensile modulus than Kevlar® 49, are used extensively in ballistic armor, asbestos replacement, and certain composites when greater damage tolerance is desired. Kevlar® 149, with a tensile modulus 25% to 40% higher than that of Kevlar® 49, is available as 1420-denier yarn. Because aramid yarns are relatively flexible and non-brittle, they can be processed in most conventional textile operations, such as twisting, weaving, knitting, carding, and felting. Yarns are used in the filament winding, prepreg tape, and pultrusion processes. Applications include missile cases, pressure vessels, sporting goods, cables, and tension members. Spun yarns Staple or short aramid fibers are available in crimped or unprimed form in lengths ranging from 6.4 to 100 mm. Spun yarns of aramid are made from Table 11.28 Kevlar® 49, 29 yarn sizes Fiber
Denier
®
Yield m/kg
yd/lb
Number of filaments
Kevlar 49
55 195 380 720 1140 1420 1860 2160 2450 2840
163636 46155 23684 12500 7895 6388 4877 4225 3673 3169
81175 22895 11749 6200 3916 3144 2400 2097 1822 1572
25 134 267 490 768 1000 1000 1000 1333 1333
Kevlar® 29
200 400 600 720 840 850 900 1000 1500 2250 3000
45000 22500 15000 12500 10714 10588 10000 9000 6000 4000 3000
22320 11160 7440 6200 5314 5252 4960 4464 2976 1984 1488
134 267 400 500 560 560 500 666 1000 1000 1333
Source: reprinted from manufacturer’s technical literature.
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377
staple fiber and are typically produced on ring spinning systems. These spun yarns are suitable for weaving or knitting various types of protective fabrics and are primarily used to knit seamless gloves and sleeves. Typically these yarns are used in the cut/thermal protection markets. Spun yarns formed in this way are not as strong or as stiff as continuous aramid filament yarns, but aramid spun yarns provide improved comfort, are bulkier, pick up more resin, and have tactile characteristics compared with filament yarns. The typical properties of Teijinconex® aramid spun yarns are listed in Table 11.29. Textured yarns Textured aramid can be processed through a high-velocity air jet to attain filament loops in the continuous filament yarn. This produces a bulkier yarn that has more air space between the filament and a drier, less slick, tactile characteristic. The yarn is used in asbestos replacement to give the composite a higher resin-to-aramid ratio and in protective apparel to achieve superior textile aesthetics.
11.6.4 Applications Aramid fibers are well known through their application in bulletproof jackets and in the automotive, electrical, electronic and medical fields. Specific uses are summarized in Table 11.30.
11.6.5 Future trends Aramid manufacturers should meet a real market need and therefore offer genuine long-term growth opportunities, integrating expertise across several areas to broaden the applications of aramid to more fields. Table 11.29 Typical properties of Teijinconex® aramid spun yarns Property
Yarn count
20.2
30.2
40.5
Allowable deviation from normal yarn count, % Variance in yarn count, % Moisture content, % Twists, turns/in. Variance in twists, % Single yarn strength, g Variance in yarn strength, % Elongation, %
1.0 1.8 5.2 15 5.1 776 7.9 22
0.7 1.9 5.0 18 4.2 492 9.3 21
1.3 2.1 5.0 21 3.7 315 10.0 17
Source: Teijin Ltd, Teijinconex Aramid Fiber, 1998.
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Technical textile yarns
Table 11.30 Applications of aramid fibers and yarns Applications
Examples
Friction materials and gaskets Prosthetics, brake linings, clutch facings, gaskets, thixotropic additive Medical applications
Prosthetics, fibrous bone cement
Optical applications
Optical fiber cables
Protective applications
Bulletproof vests, helmets, vehicle protection, firefighting, cut protection, ballistics, heat resistant workwear, flame-retardant textiles
Composites
Tires, pipes, pressure vessels, plastics additive, civil engineering
Ropes and cables
Ignition cables, aerial optical fiber cable, electrocable, mooring ropes
Sporting equipment
Sailcloths, tennis strings
Source: authors’ summary.
H
H
C
C
H
H n
11.15 Ultra-high molecular weight polyethylene (UHMWPE).
11.7
High-performance polyethylene (HPPE) fibers and yarns
11.7.1 Composition and structure High-performance polyethylene fibers are produced from ultra-high molecular weight polyethylene (UHMWPE). This substance has extremely long chains, with molecular weight numbering in the million, usually between 2 and 6 millions. Its chemical formula is shown in Fig. 11.15. This material is chemically identical to normal polyethylene, but its molecular weight is much higher than the commonly used PE grades. Polyethylene has longer and more flexible molecules and through physical treatments the molecules can be forced into a straight conformation and orientation in the direction of the fiber. When formed into HPPE fibers, the polymer chains can attain a parallel orientation greater than 95% and a level of crystallinity of up to 85% as shown in Fig. 11.16. Advantage can be taken of the long length of the molecules in UHMWPE to make fibers with high strength and high tensile stiffness [38]. Finished UHMWPE is produced by
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High modulus, high tenacity yarns High performance polyethylene
Regular polyethylene
Orientation > 95% Crystallinity up to 85%
Orientation low Crystallinity < 60%
379
11.16 Macromolecular orientation of HPPE and normal PE (reproduced from Ref. 38).
four major methods: compression molding, ram extrusion, gel spinning, and sintering.
11.7.2 Properties At present, HPPE fibers are produced commercially by Allied Signal (Spectra®), DSM High Performance Fibers, and the Toyobo Company (Dyneema®). These products are all made by the gel-spun process. Physical properties HPPE fibers have a density of 970 to 980 kg/m3 [39] which is lower than that of water, so that they float in water. Most fiber grades have a more or less circular cross-section and the fiber skin is smooth. The mechanical properties of commercial HPPE fibers are listed in Table 11.31. The primary properties of Dyneema® and Spectra® are high strength and high modulus in combination with low density. This remarkable fiber is up to 15 times stronger than steel and, weight-for-weight, 40% stronger than competing aramid fibers. The combination of high strength with low density makes the specific strength or tenacity and specific modulus extremely high. Elongation at break is relatively low, as for other high-performance fibers, but owing to the high tenacity, the energy to break is high. In contrast to the high tensile strength, the gel-spun fiber has low compressive yield strength, approximately 0.1 N/ tex [38]. As all the chains in the fiber are aligned in the fiber direction, the mechanical properties are highly anisotropic. In the transverse direction the
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Technical textile yarns
Table 11.31 Mechanical properties of commercial HPPE fibers Dyneema, DSM Dyneema, Toyobo
Spectra, Honeywell (formerly Allied signal)
Type Strength (GPa) Young’s modulus (GPa) Elongation (%)
3.9
SK60 SK65 SK75 SK76 SK60 SK71 900 1000 2000 2.7 3.0 3.4 3.6 2.8 4.0 2.57 3.25 3.34 89 95 107 120 94 120 73 113 124 3.5
3.6
3.8
3.8
3.5
3.7
2.9
3.0
Source: reprinted from manufacturer’s technical literature. Table 11.32 Transverse properties of HPPE fibers Transverse elastic modulus Transverse compressive yield stress Transverse tensile strength
3 GPa 0.05 GPa 0.03 GPa
Source: Ref. 38.
modulus and strength are much lower than that in the fiber direction. Table 11.32 gives estimated values [38]. Another feature is that the fiber is prone to creep. The high molecular weight polyethylene used for HPPE fibers is also a well-known engineering plastic. As such it is used especially for its superior wear and abrasion resistance. Dyneema® and Spectra® fibers can absorb extremely high amounts of energy due to the high elongation to break in combination with the high modulus. This property is utilized in products for ballistic protection but makes the fiber equally suited for products such as cut-resistant gloves and motor helmets. The fibers can also be used to improve the impact strength of carbon or glass fiber-based composites. These applications make use of not only the high tenacity but also the high energy absorption. HPPE fibers are the first high-performance fibers that have not only high tenacity but also tension and bending fatigue properties comparable with the commonly used polyamide and polyester grades in ropes. Carbon fibers and glass fibers have a high modulus and a brittle breaking mode, but HPPE fibers demonstrate that this is not an obvious combination. Chemical resistance HPPE fibers are produced from polyethylene and do not contain any aromatic rings or any amide, hydroxylic or other chemical groups that are susceptible to attack by aggressive agents. The result is that polyethylene and especially highly crystalline, high molecular weight polyethylene is very resistant against chemicals.
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Electrical properties Polyethylene is an insulator and has no groups with dipole character. The fiber is characterized by a high resistivity (volume resistivity > 1014 Wm), a low dielectric constant (2.25) and a very low dielectric loss factor (2 ¥ 10–4). Thermal properties The relatively low melting temperature makes the fiber sensitive to warming up due to hysteresis losses. Dyneema® has a melting point between 144 and 155°C, depending on the conditions, the higher temperature being measured if the fiber is constrained. The tenacity and modulus decrease at higher temperatures but increase at sub-ambient temperatures. There is no brittle point down to 4 K (–269°C), so the fiber can be used from cryogenic conditions up to a temperature of 80–100°C. Brief exposure to higher temperatures, but below the melting temperature, will not cause any serious loss of properties.
11.7.3 Commercial products of HPPE yarns Commercially produced gel-spun fibers have been on the market since 1985. Commercial HPPE fibers are always supplied in the form of rovings and these rovings can further be used in the production of rope. Dyneema® yarn is a roving supplied in a number of yarn grades as shown in Table 11.31. This multi-purpose grade of SK25/SK60/SK65 is ideal for many applications, including ropes, fishing nets, cordage, protective clothing and to reinforce impact-resistant semi-structural composites. SK75, with a higher tenacity than SK60 (25% stronger), is specially designed for use in ropes, cordage, fishery and textile applications, wherever higher performance and maximum weight savings are required. Dyneema® yarn is normally supplied without twist but if required it can be supplied as twisted yarn. Spectra® fiber is also supplied as rovings which have many applications in numerous high-performance applications, including police and military ballistic-resistant vests, helmets and armored vehicles, as well as sailcloth, fishing lines, marine cordage, lifting slings, and cut-resistant gloves and apparel.
11.7.4 Applications Most applications of HPPE are either in ropes and nets or in products for ballistic protection. Table 11.33 gives a more detailed summing up of the applications of gel-spun UHMWPE fibers.
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Table 11.33 Applications of HPPE fibers and yarns Ropes and cordage
Ballistic protection
Others
Towing lines Mooring/anchor lines Yacht ropes Twines Trawl nets Fishing line Parapent lines
Bulletproof vests Inserts for vests Military helmets Car armor panels Vehicle armor panels Ballistic blankets Storm protection panels
Medical devices Sail Cut-resistant gloves Radomes Dental floss Textiles Composites
Source: authors’ summary.
11.7.5 Future trends A characteristic of gel-spun UHMWPE fibers is that plastic deformation is still possible, either as slow deformation at relatively low temperature (creep), or relatively fast at elevated temperature. This means that UHMWPE fibers are short-term in application, limiting the range of possible applications. Methods to overcome these disadvantages would be a beneficial future trend.
11.8
Sources of further information and advice
11.8.1 General comments and suggestions High modulus, high tenacity yarns have been widely used in industry. Therefore, there is a large amount of technical literature in the websites of manufacturers and research organizations and among conference proceedings. Furthermore, Woodhead Publishing and other companies have published many books about high performance fibers and their composites.
11.8.2 Books for further reading
1. 2. 3. 4. 5. 6. 7.
High Performance Fibres, Woodhead Publishing, 2001. High Performance Polymers, William Andrew Publishing, 2008. Carbon Fibers and their Composites, CRC Press, 2005. Carbon Fiber Composites, Butterworth-Heinemann, 1994. Carbon Fibers, Marcel Dekker, 2007. Ceramic and Glass Materials, Springer Verlag, 2008. Encyclopedia of Materials Science and Technology, Pergamon, 2001. 8. Fiber-Reinforced Composite Materials, Manufacturing, and Design, CRC Press, 1993. 9. Handbook of Composite Reinforcements, John Wiley and Sons, 1992.
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10. Handbook of Fibre Rope Technology, Woodhead Publishing, 2004. 11. Handbook of Materials for Product Design, McGraw-Hill Professional, 2001. 12. Handbook of Technical Textiles, Woodhead Publishing, 2000. 13. Textiles for Protection, Woodhead Publishing, 2005. 14. Comprehensive Composite Materials: Volume 1 Fiber Reinforcements and General Theory of Composites, Pergamon, 2000. 15. Yarn Texturing Technology, Woodhead Publishing, 2001. 16. Handbook of Ceramic Composites, Boston Kluwer Academic Publishers, 2005.
11.8.3 Manufactures’ websites Glass fibers AGY, Inc., http://www.agy.com/ Johns Manville, Inc., http://www.jm-reinforcement.com/ NGF EUROPE, Inc., http://www.ngfeurope.com/ Carbon Polycarbon, Inc., http://www.polycarbon.com/ Toho Tenax, Inc., http://www.tohotenaxamerica.com/index.php Toray Industries, Inc., http://www.toray.com/ Hexcel, Inc., http://www.hexcel.com/ Cytec Industries, Inc., http://www.cytec.com/index.htm Asahi Kasei, Inc., http://www.ak-america.com/index.php Grafil, Inc., http://www.grafil.com/ Zoltek Companies, Inc., http://www.zoltek.com/ SGL Group the carbon, Inc., http://www.sglgroup.com/ AKZO Fortafil Fibers, Inc., http://www.akzonobel.com/ Ceramic 3M Nextel, http://www.3m.com/market/industrial/ceramics/ ICI Saffil, http://www.saffil.com/newwebsite.nsf Nippon Carbide, http://www.carbide.co.jp/EN/index_top.html Basalt BFCMTD, http://www.basaltfm.com/index.html Kamenny Vek, http://www.basfiber.com/ LBIE, http://www.lbie.com/n3011.htm
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Aramid DuPont Kevlar, http://www2.dupont.com/Kevlar/en_US/index.html DuPont Nomex, http://www2.dupont.com/Nomex/en_US/ Teijin, Ltd, http://www.teijinaramid.com/ HPPE DSM, http://www.dsm.com/en_US/html/hpf/home_dyneema.htm Allied Signal, http://www51.honeywell.com/honeywell/
11.9
References
1. S K Mukhopadhyay, ‘High-performance fibers’, Textile Progress, 1993, 25, 1–85. 2. F R Jones, ‘Glass fibres’, in High Performance Fibres, ed. J W S Hearle, Cambridge, Woodhead Publishing, 2001, pp. 191–238. 3. D R Hartman, M E Greenwood and D M Miller, ‘High strength glass fibers’, Owens Corning, Inc., technical paper ref. 1-Pl-19025-A, July 1996. Reprinted by AGY LLC as Pub. No. LIT-2001-011 (05/01), May 2001. 4. K. Loewenstein, The Manufacturing Technology of Continuous Glass Fibers, 3rd edn, Amsterdam, Elsevier Science, 1993. 5. D W Dwight ‘Glass fiber reinforcements’, in Comprehensive Composite Materials Volume 1, eds A Kelly and C H Zweben, Amsterdam, Elsevier Science, 2000, pp. 231–261. 6. ‘Standard Test Method for Density of Glass by Buoyancy’, C693, in Annual Book of ASTM Standards, American Society for Testing and Materials. 7. G Lewis, S W Bedder and I Reid, J. Mater. Sci. Lett., 1984, 3, 728–732. 8. ‘Standard Test Methods for Coefficient of Linear Thermal Expansion of Plastics’, D 696, in Annual Book of ASTM Standards, American Society for Testing and Materials. 9. ASTM D 578, ‘Standard Specification for Glass Fiber Strands’, American Society for Testing and Materials. 10. D B Miracle, ASM Handbook: Composites, ASM International, 2001. 11. H A McKenna, J W S Hearle and N O’Hear, Handbook of Fibre Rope Technology, Cambridge, Woodhead Publishing, 2004. 12. J G Lavin, ‘Carbon fibres’, in High Performance Fibres, ed. J W S Hearle, Cambridge, Woodhead Publishing, 2001, pp. 156–190. 13. S Yamane, A T Hiramatsu and T Higuchi, in Proceedings of the 32nd International SAMPE Symposium, Anaheim, CA, eds R Carson, M Burg, K J Kjoller and F J Riel, SAMPE, Covina, CA, 1987, pp. 928–937. 14. ‘Testing methods for carbon fibers (Amendment 1)’, JIS R 7601:1986/Amendment 1:2006, Japanese Industrial Standard. 15. S R Allen, J. Mater. Sci., 1987, 22, 853–859. 16. V V Kozey, H Jiang, V R Mehta and S Kumar, J. Mater. Res., 1995, 10, 1044– 1061. 17. S Kumar, D P Anderson and A S Crasto, J. Mater. Sci., 1993, 28, 423–439.
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18. K Matsubara, N Ohba, K Kawamura, T Tsuzuku and K Sugihara, in Extended Abstracts of the 22nd Biennial Conference on Carbon, San Diego, CA, American Carbon Society, University Park, PA, 1995, pp. 704–705. 19. C Gourdin, ‘Ageing of carbon fibers of various origins’, SAMPE, Bordeaux, 17–20 October 1983, pp. 49–61. 20. T Ishikawa, S Kajii, T Hisayuki and Y Kohtoku, ‘New type of SiC-sintered fiber and its composite material’, Ceram. Eng. Sci. Proc., 1998, 19(3), 283–290. 21. J Lipowitz, J A Rabe, A Zangvil and Y Xu, ‘Structure and properties of Sylmaric silicon carbide fiber – A polycrystalline, stoichiometric b-SiC composition’, Ceram. Eng. Sci. Proc., 1997, 18(3), 147–157. 22. S Yajima, X Hasegawa, J Hayashi and M Iiuma, ‘Synthesis of continuous silicon carbide fiber with high tensile strength and high Young’s modulus’, J. Mater. Sci., 1978, 13, 2569–2576. 23. T Yamamura, T Ishikawa, M Shibuya, T Hisayuki and K Okamura, ‘Development of a new continuous Si-Ti-C-O fibre using an organometallic polymer precursor’, J. Mater. Sci., 1988, 23, 2589–2594. 24. M Takeda, Y Imai, H Ichikawa, T Seguchi and K Okamura, ‘Properties of the low oxygen content SiC fiber on high temperature heat treatment’, Ceram. Eng. Sci. Proc., 1991, 12(7,8), 1007–1018. 25. H Ichikawa, K Okamura and T Seguchi, ‘Oxygen-free ceramic fibers from organosilicon precursors and e-beam curing’, Proc. Conf. High Temperature Ceramic Matrix Composites II, ed. A G Evans and R Naslain, Ceramic Transactions, The American Ceramic Society, 1995, 58, 64. 26. A K Dhingra, ‘Alumina fiber FP’, Phil. Trans. R. Soc. Lond., Ser. A, 1980, A294, 411–417. 27. B Cantor, F P E Dunne and I C Stone, Metal and Ceramic Matrix Composites, Institute of Physics (Great Britain), 2003. 28. A K Dhingra, Phil. Trans. R. Soc. Lond., Ser. A, 1980, A294, 411–417. 29. Y Saitow, K Iwanaga, S Itou, T Fukumoto and T Utsunomiya, ‘Preparation of continuous high purity a-alumina fibers’, Proc. 37th Int. SAMPE Symp., 9–12 March 1992, pp. 808–819. 30. D M Wilson, D C Lueneburg and S L Lieder, ‘High temperature properties of Nextel 610 and alumina based nano-composite fibers’, Ceram. Eng. Sci. Proc., 1993, 14, 609–621. 31. J D Birchall, ‘The preparation and properties of polycrystalline aluminium oxide fibers’, Trans. J. Br. Ceram. Soc., 1983, 82, 143–145. 32. Y Abe, S Horikiri, K Fujimura and E Ichiki, in Progress in Science and Engineering of Composites, eds T Hayashi K Kawata and S Umekawa, Japan Soc. Comp. Mat., 1982, pp. 1427–1434. 33. S Ozawa, ‘A new approach to high modulus, high tenacity fibers’, Polymer Journal, 1987, 19(1), 119–125. 34. S Rebouillat, ‘Aramids’, in High Performance Fibres, ed. J W S Hearle, Cambridge, Woodhead Publishing, 2001, pp. 23–61. 35. A E Zachariades and R S Porter, The Strength and Stiffness of Polymers, New York, Marcel Dekker, 1983, p. 327. 36. R J Morgan, C O Pruneda, N Butler, F M Kong, L Caley and R I Moore, in SAMPE Meeting, Reno, NV, SAMPE, Covina, CA, 1984. 37. H H Yang, ‘Aramid fibres’, in Comprehensive Composite Materials Volume 1, eds A Kelly and C H Zweben, Amsterdam, Elsevier Science, 2000, pp. 199–229.
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38. J L J Van Dingenen, ‘Gel-spun high-performance polyethylene fibres’, in High Performance Fibres, ed. J W S Hearle, Cambridge, Woodhead Publishing, 2001, pp. 62–92. 39. T Peijs, M J N Jacobs and P J Lemstra, ‘High performance polyethylene fibers’, in Comprehensive Composite Materials Volume 1, eds. A Kelly and C H Zweben, Amsterdam, Elsevier Science, 2000, pp. 263–301.
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Hybrid yarns for thermoplastic composites
R. A l a g i r u s a m y, Indian Institute of Technology, Delhi, India
Abstract: In recent years, the use of textile structures made from high performance fibers is finding increasing importance in composites applications. In the textile process, there is direct control over fiber placements and ease of handling of fibers. Besides economic advantages, textile technologies also provide a homogeneous distribution of matrix and reinforcing fiber. Various types of hybrid yarns for thermoplastic composites and textile preforming methods are discussed in detail in this chapter. Information on manufacturing methods, structural details and properties of different hybrid yarns are presented and critically analyzed. Characterization methods used for these hybrid yarns are discussed along with the influence of different processing parameters on the properties being characterized. Key words: hybrid yarns, thermoplastic composites, commingling, consolidation, fiber matrix distribution.
12.1
Introduction
Throughout the last two decades, fiber reinforced composite materials were principally fabricated using thermosetting matrices. Disadvantages stemming from the use of thermoset resins include brittleness, lengthy cure cycles and inability to repair and/or recycle damaged or scrapped parts. These disadvantages led to the development of the thermoplastic matrix composite system. For these reasons, thermoplastic polymers have emerged as strong competitors for the traditional thermoset matrix materials. Advanced thermoplastic composites had attracted increasing interest in the composite industry since they were first commercialized in the late seventies. Thermoplastic composites can provide several advantages over thermoset composites in terms of mechanical properties and processing. Thermoplastic polymers are distinguished by their ability to be reshaped upon the addition of heat. This cycle can be carried out repeatedly. Thermosetting polymers, on the other hand, undergo chemical reactions during curing which crosslink the polymer molecules. Once crosslinked, thermoset resins become permanently hard and simply undergo chemical decomposition under the application of excessive heat. Thermosetting polymers typically have greater abrasion resistance and dimensional stability over those of thermoplastic polymers, which usually demonstrate better flexural and 387 © Woodhead Publishing Limited, 2010
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impact properties. Thermoplastic molecules are associated with physical intermolecular forces, whose molecular segments can move under stress, while thermoset resins are tied up by dense crosslinking bonds and thus are more rigid. Hence, thermoplastic composites usually have higher strains at failure than thermoset composites, and thus possess better fracture toughness and fatigue endurance. Thermoplastic composites typically require a shorter and simpler processing cycle, as their processing mainly deals with heating and cooling of matrix material and involves no chemical reactions. For this reason, thermoplastic composites offer new opportunities for fast and efficient processing technology. However, as in many polymer composite systems, these materials frequently suffer from a lack of adequate fiber–matrix adhesion. In addition, the use of thermoplastics introduces the problem of inadequate resin penetration into the fiber tow. Thermoplastic melts, as opposed to thermosetting resins, have a substantially higher viscosity. Due to the high viscosity, it is very difficult to inject the resin into a tightly woven textile structure and to fill its pores created by the fiber interlacement. This problem increases the void content in the composite material, which can be overcome using high levels of injection pressure and heavier molds. Thermoplastic matrices must be able to withstand high temperatures during consolidation in order to effect a sufficient reduction in viscosity. Additional problems caused by high matrix viscosity during consolidation include de-alignment of reinforcing fibers during consolidation as well as the introduction of voids within the final composite product. These problems may be alleviated by reducing the melt flow distance during consolidation process. Composites prepared with satisfactory matrix dispersion within the fiber tows as well as reasonable fiber–matrix adhesive interaction have good mechanical properties. To solve this problem, the matrix polymer needs to be mixed with high performance fibers even before the preforming operation. There are several techniques such as hot melt, film, solution, emulsion, slurry, surface polymerization, the commingling and dry powder coating. Out of these methods, some methods such as commingling and powder coating have the potential for producing prepregs with considerable flexibility, which is a critical requirement for textile processing. In this chapter, the thermoplastic prepregs having sufficient flexibility to go through textile preforming without getting damaged significantly are considered as thermoplastic hybrid yarns. In thermoplastic hybrid yarns, when heat is applied, the thermoplastic component melts and impregnates the reinforcing component and forms an amorphous reinforcing binder. After subsequent cooling, the system is transferred into a rigid composite material. A homogeneous distribution of reinforcement and matrix would reduce the mass transfer distance of the
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matrix during processing, which will lead to a fast and complete impregnation of the reinforcement filaments.
12.2
Types of hybrid yarns
Hybrid yarns can be manufactured in different ways including co-wrapping, core spinning and commingling, aiming to give a uniform distribution of matrix and reinforcement fibers as well as to reduce the damage to reinforcing fibers. In co-wrapping, thermoplastic fibers are wrapped around a core of reinforcing fibers. This provides better protection for the reinforcing fibers during further processing such as weaving or braiding. However, inhomogeneous distribution of the reinforcing and matrix yarns may lead to poor impregnation and does require higher processing temperatures and pressures [1]. In friction spinning or core spinning, short thermoplastic fibers are spun around a core of continuous reinforcing fibers. The properties of these yarns are comparable with those of the co-wrapped yarns. These yarns are very flexible and make further processing easier. Coldicott and Longdon [2] described the ‘Heltra’ process, a stretch breaking technique, to develop hybrid yarns. In this process, yarns consisting of discontinuous fibers are bound together into a well-oriented coherent bundle by insertion of a degree of twist. This technology also produces highly consistent yarns with minimal fiber damage. Both single component and blended multi-component yarns can be developed by this technique. In commingling, the reinforcing and matrix fibers are intimately mixed in a nozzle by means of compressed air. Among these hybrid yarns, commingled yarns provide high potential for thorough blending of matrix-forming filaments and high performance fibers. This process is versatile and gives soft, flexible and drapable yarn. This has made commingling technology suitable for the textile preforming process to produce high performance composites [3]. Combination of commingling and co-wrapping may give a yarn with very good matrix/reinforcement distribution and good protection of the reinforcing fibers. Although the commingling technique has the potential to produce towpregs with good blending, these towpregs tend to de-mingle under load and during the preforming operation. Commingling and air-jet texturing techniques work on similar principles using air jets and both of these techniques have been tried out to blend high performance filaments and matrix-forming filaments for composite applications. The principles of operation of these two techniques and work performed using techniques for composite applications are discussed. Commingled yarn consists of a blended combination of reinforcing filament yarn and filament yarn spun from thermoplastic polymers. The multifilament yarns are distributed amongst one another at filament level. By using the
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commingling process any weavable reinforcing fiber and most spinnable polymeric fibers can be combined. Good processability of the commingled hybrid yarns by almost all known textile-manufacturing technologies is a further advantage. In combination with developments in textile structures, the use of commingled yarns significantly improves the mechanical properties of resultant composite parts. Studies on commingled composites with different reinforcing fibers and matrix material combinations are reported in the literature [2]. Apart from the above techniques, thermoplastic hybrid yarns can be produced through yarn manufacturing processes like ring spinning, rotor spinning, wrap spinning, friction spinning and other techniques. The details of the above techniques and hybrid yarns produced with these techniques are discussed in the following sections.
12.2.1 Ring spinning Existing ring spinning techniques cannot be used to manufacture hybrid yarns without modifications at the process level. In its conventional form, this technique is used to spin spun yarns from staple fibers using a pair of rollers for the drafting and set of components, namely spindle, ring and traveler, for twisting and winding. With slight modifications and little investment, this technique can be suitably used to produce hybrid yarns by the core spinning system. In addition to the conventional creel of the ring frame, another creel to support the filament yarn is required along with tensioning and guide arrangements to position the filament correctly. The filament is pulled over from the creel and fed to the nip of the front drafting rollers. Thus the front drafting roller receives a continuous filament as well as a drafted strand of roving. These are twisted together upon delivery from the front drafting roller and wound onto the package. The filament guide and the roving guide are held on the same bar, thereby giving the same to-and-fro motion to the filament to that of roving. Audivert and Fortuny [4] used this technique to produce core spun yarns satisfactorily. Optimization of filament pre-tension is one of the most important aspects of core spinning because adequate tension helps the core component to adapt the axial position and to be well covered. A common problem with core spun yarns made on a ring spinning frame is the slippage of the staple fibers relative to the filament, which gives a length of bare filament with a clump of fibers at one end. This effect is known as ‘strip-back’ or ‘barberpole’ [5]. This fault may lead to incomplete core coverage and results in end break in the subsequent processing. Thus, a rather high level of twist is normally needed to build up the necessary cohesion between the sheath and the core components. The high twist reduces the production speed and thereby
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increases the production costs. The high level of twist is also not desirable for composite applications, as this would lead to more breakage of high performance filaments in the core and also more drop in the axial properties of the composites. Oxenham et al. [5] described a filament-charging device based on the principle of a two-electrode system to separate a multi-filament yarn. The continuous filament yarn is first electrically charged by contacting the top electrode, so that the individual filaments constituting the yarn tend to repel one another because they all carry the same charge. Furthermore, owing to the action of the electric field established between the electrodes, there is an attraction between the charged filaments and the lower electrode, reinforcing the tendency for the filaments to be pulled outwards to form a balloon-like shape. The separated filaments were then mixed with the staple fibers of a roving at the roller nip. The blended ribbon was subsequently twisted to form a yarn. Though the unique properties of yarns produced with many improved methods are impressive, the economic viability of the methods is limited by the inherently low productivity and relatively high cost of ring spinning. Commercial twisting has been reported to be used for the production of hybrid yarns for thermoplastic composites. In a US patent [6], O’Connor produced three-ply hybrid yarn by twisting two plies of 850 denier poly(phenylene sulfide) yarn and one ply of 1717 denier carbon fiber yarn at a low twist of 2.5 TPI.
12.2.2 Rotor spinning Pouresfandiari et al. [7] have described a mechanical hybrid core-spun yarn spinning system that produces different yarns on a modified open-end rotor spinning frame. It was claimed that core spun and cover-spun hybrid yarns can be produced by combining staple fibers with filament yarns under varying filament overfeeds. For this work, cotton sliver as the staple fiber and a polyester filament as the continuous filament were fed into the rotor. Yarns were produced with different overfeeds on an experimental open-end rotor spinning frame equipped with a BD 200 rotor spin box. This technology again has a tendency to introduce filament misalignment in the core yarn which is not preferable for composite application.
12.2.3 DREF spinning This spinning system is used largely for the manufacture of core spun hybrid yarns for thermoplastic composites. The principle of friction spinning on which the DREF spinning system works is shown in Fig. 12.1a. In its conventional form, the completely opened fiber strand is brought into engagement with
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Winding device
Air current Card + drum
Parallelizer
Inlet system Outlet roller
Spinning drum
(a)
Matrix-forming fibers (b)
Reinforcing filaments
12.1 (a) DREF spinning system; (b) schematic of structure of DREF spun yarn.
the rotating open end of the yarn by a perforated drum. Binding in of fibers and imparting strength are effected by continual rotation of the yarn in the converging region of the two drums. The rotation of the yarn arises from the rotary movement of the two drums and is generated by frictional contact at the drum surface. The yarn formed is constantly withdrawn and wound on a package. This system can be used to manufacture a hybrid yarn with core/sheath structure consisting of reinforcing filaments of high performance fibers in the core, surrounded by the staple fibers of thermoplastic matrix material in the sheath. In an effort to manufacture hybrid yarns through friction spinning, the Institute for Textile Technology has modified the DREF-3 spinning machine, and the yarn structure thus obtained is depicted in Fig. 12.1(b). A glass, carbon
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or aramid filament yarn can be fed in a rectilinear way via a tensioning unit into a spinning device. The straight path of the yarn ensures that no filament damage occurs. Above the friction drums there is a drafting device with an opening unit. Here, the material to cover filaments is supplied as slivers. Polyester, poly-ether-ether-ketone or liquid crystal polymers may be used. In the gusset between the two friction drums, spinning takes place, covering the filament yarn completely with thermoplastic staple fibers. The core–cover ratio can be adjusted in a wide range. Since filament yarns are used untwisted and completely straightened, their maximum strength potential is realized.
12.2.4 Wrap spinning The principle of wrap spinning used to manufacture wrap spun yarns is shown in Fig. 12.2(a) [8]. A strand of one type passes through a hollow spindle without receiving true twist. A continuous filament thread from the package mounted on the hollow spindle is made to pass through the hollow spindle as shown. Thus this filament strand is wound around the twistless strand in the core. Abbott and Freischmidt [9] used this technique to manufacture wrapped yarns as reinforcement in composites. This system, with minor changes, can be used to manufacture hybrid yarns wherein both the components are in the filament form. The reinforcing filament is wrapped around by the thermoplastic matrix filaments. The yarn structure obtained by wrap spinning is shown in Fig. 12.2(b). These wrapping filaments can be matrix-forming filaments or any other fine filament yarns. In case of matrix-forming filaments, these filaments will melt during the consolidation process and become part of the matrix. In other cases, they will remain in the final composite in their original form. Hence, they need to be very fine yarns so that the interface between the reinforcing filaments and the matrix is not affected to a significant level. This provides a better protection for the reinforcing fibers during further processing, such as weaving or braiding. However, inhomogeneous distribution of the reinforcing and matrix yarns may lead to poor impregnation and requires higher processing temperatures and pressures.
12.2.5 Air-jet texturing Air-jet texturing is a purely mechanical process that can be used to combine reinforcing and matrix-forming filaments. Figure 12.3(a) shows the schematic of the air-jet texturing process, and the structure of the air-textured yarn is shown in Fig. 12.3(b). In this process, supply yarn is overfed in the turbulent zone where compressed air is directed mainly parallel to the yarn path, resulting in shifting of filaments longitudinally together with the formation of filament loops. This action opens up filament bundles, and then builds
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Drafting
Wrapping
Delivery (a)
Matrix filaments
Wrapping filaments (b)
Reinforcing filaments
12.2 (a) Filament wrapping system; (b) schematic of structure of filament wrapped yarn.
mingling sections. The heart of the air-jet texturing process is the air nozzle. The purpose of the nozzle is to create a supersonic, turbulent and non-uniform flow to entangle or blend the filaments, forming them into loops to produce stable textured yarns. Some texturing nozzles have an impact element of different sizes and shapes at the exit of the nozzle, aiming to improve process stability and quality of textured yarns [10]. A single yarn or two or more yarns of the same or different types can be
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(a)
Matrix filaments
(b)
Reinforcing filaments
12.3 (a) Principle of air-jet texturing system; (b) schematic of structure of air-jet textured yarn.
textured at the same speed (parallel end texturing) or co-textured at different speeds (core and effect texturing) by the use of separate feed rollers to facilitate blending of different types of filament yarns during processing. The effects of various combinations of polymers with different shrinkage potentials, deniers, tensile properties and cross-sectional shapes on the loop formation mechanism have been reported [11]. The mechanism of loop formation with particular reference to filament interactions with compressed air in the air nozzle has been investigated in detail [12]. Kothari et al. [11] studied the loop formation process and observed that ‘turbulent, asymmetric fluid forces in association with intermittent compression shock waves open up the filaments and blow the overfed lengths out of the texturing nozzle at speeds much greater than the delivery speed of the yarn. The difference in the speed between leading and trailing ends of the section of filaments under the action of fluid forces causes bending of filaments in the form of loops and arcs’. Acar and Wray [12] analyzed a short incremental section of a single filament subjected to the airflow in the texturing nozzle. They observed that the drag force acting on the filament is a function of local air velocity, filament surface and the projected areas
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exposed to the flow, commenting that the surface and projected areas of the filaments exposed to the flow are determined by the position of filaments across the nozzle, the cross-section and the orientation of the filaments. Acar et al. [10] also investigated the airflow profile in texturing jets and its effect on individual filaments, on the generation of shock waves and on changes in yarn tension. They observed that individual filaments separate and change their positions across the nozzles at very high frequencies; some of the filaments move instantaneously faster than others due to non-uniform velocity distributions, causing the filaments to bend and entangle among themselves. Bock and Lunenschloss [13] gave evidence of an asymmetric airflow outside the jet and commented that the asymmetry of flow alters the forces acting on the separated individual filaments which in turn cause longitudinal displacement of the filaments relative to each other. The authors also observed that the generation of shock waves depends on the nozzle type and these shock waves would be destroyed during the actual texturing process.
12.2.6 Commingling In the mingling process, rapidly moving air in an air jet is used to generate entanglements in and among filaments. Figure 12.4(a) shows the schematic of the intermingling process and the structure of intermingled yarn. Synonyms to the term mingling used in industry are interlacing, tangling, entangling, intermingling and commingling. A mingling process of two or more yarns to form a single strand of yarn can be defined as commingling. Commingled yarn consists of a blended combination of reinforcing filament yarn and filament yarn spun from thermoplastic polymers as represented by Fig. 12.4(b). The multifilament yarns are scattered amongst one another at filament level. By using a commingling process any weavable reinforcing fiber and most spinnable polymer fibers can be combined. A homogeneous distribution of reinforcement and matrix would reduce the mass transfer distance of the matrix during processing, which leads to a fast and complete impregnation of the reinforcement filaments. The desired ratio of fiber to matrix can be achieved by varying the number of constituent yarns during hybrid yarn production itself. Good processability of the commingled hybrid yarns by almost all known textile-manufacturing technologies is a further advantage. In combination with developments in textile structures, the use of commingled yarns significantly improves the mechanical properties of the resultant composite parts. Several patents have been claimed on commingling of high performance and matrix-forming filaments for composites and other applications. One patent [14] describes GF/PTFE commingled yarns, which are far more resistant to flex, abrasion and chemical attack than fiberglass fibers. The filaments of
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(a)
Matrix filaments
(b)
Reinforcing filaments
12.4 (a) Principle of intermingling system; (b) schematic of structure of commingled yarn.
expanded PTFE tow yarn and filaments of PTFE are combined through a process of air-jet texturing. The patent also claimed use of other yarns such as polyphenylene sulfide (PPS) to develop commingled yarns. Another patent [15] describes a method and an apparatus whereby continuous filaments are crimped and then commingled to form a variable textured yarn. A third patent [16] describes the use of a commingled yarn with slight twist to the tune of 0.2–0.8 turns/cm. This twist assists in prepreg manufacturing by various techniques like weaving/braiding, etc. Another patent is also available on the method for commingling and orienting colored sets of thermoplastic filaments [17] and on the process for commingling crimped yarns.
12.2.7 Parallel winding In this much simpler process, two components of hybrid yarns, i.e. reinforcing filaments and matrix-forming filaments, are led side by side to each other [1] as shown in Fig. 12.5(a).
12.2.8 Stretch breaking Coldicott and Longdon [2] described the ‘Heltra’ process, a stretch breaking technique to develop hybrid yarns. In this process, yarns consisting of © Woodhead Publishing Limited, 2010
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Matrix filaments
(a)
Reinforcing filaments
(b)
Matrix filaments
Matrix filaments
Knitted sheath (c)
(d)
Reinforcing filaments
Reinforcing filaments
12.5 Structures of (a) side-by-side yarns, (b) Heltra stretch broken yarn, (c) Kemafil yarn, (d) Schappe yarn.
discontinuous fibers are bound together into a well-oriented coherent bundle by the insertion of a degree of twist. This technology also produces highly consistent yarns with minimal fiber damage. Both single-component and
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blended multi-component yarns can be developed by this technique. The structure of this yarn is shown in Fig. 12.5(b).
12.2.9 Kemafil technology This technology has been developed by Saxon Textile Research Institute, Chemnitz, Germany. This is a turning thread technique. By means of mechanical interlacing of yarns into a knitted structure, linear textiles are produced. Kemafil machines are circular knitting machines operating with loopers that are arranged around a guide bar and give a tubular knitted structure which can cover any type of core yarn. In this type of hybrid yarns, a parallel arrangement of matrix fibers is surrounded by parallel reinforcing filaments. This entire structure of matrix and reinforcing filaments is placed in the core in a sheath of matrix fibers in the skin [1]. The yarn structure is shown in Figure 12.5(c).
12.2.10 Schappe technology These types of hybrid yarns are composed of a mixture of discontinuous reinforcing and matrix filaments surrounded by continuous matrix filaments [1]. The yarn structure is shown in Fig. 12.5(d).
12.2.11 Braided yarn Sakaguchi et al. [18] manufactured unidirectional thermoplastic composites from micro-braided yarns. Figure 12.6 provides a photograph and schematic drawing of a micro-braided yarn. Micro-braided yarns in this study consisted of tubular-braided fabrics (the braiding technique is discussed in the preforming section). Micro-braided yarns consist of reinforcing fiber and thermoplastic resin. The authors produced different types of micro-braided yarns by varying the type and the number of braiding fiber bundles, middle end fibers Middle end fiber
Type M
Type M
12.6 Structures of micro-braided yarns.
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and axial fibers. Braiding of several fibers together for the production of hybrid yarns for thermoplastic composites has been described in US patent 4800113 [6].
12.3
Characterization of hybrid yarns
The structure and form assumed by the hybrid yarn in preforms have considerable effect on preform properties such as drape, wrinkling, flexibility, permeability and thickness. Eventually these properties are very important during forming of composites from textile preforms. The geometry and structure of textile preforms can be tailored by desired modifications in structure and properties of fibers as well as yarns. Therefore, it is extremely important to understand the behavior of hybrid yarns in subsequent processing. Hybrid yarns are characterized by their properties like tensile strength, bending stiffness, friction, compression resilience and their processing characteristics like braidability, molding characteristics and resin flow distance.
12.3.1 Structure and properties of hybrid yarns The parameters which influence the structure and properties of hybrid yarns can be divided into the following two groups: ∑ ∑
Raw material parameters such as filament linear density, number of filaments, cross-sectional shape of fibers, filament rigidity, and frictional characteristics of filaments The kind of process and the process parameters used to manufacture the hybrid yarns.
The influence of these variables on the structure and properties of hybrid yarns is discussed below.
12.3.2 Friction, flexibility and compressive properties The smooth operation of any preform manufacturing process such as braiding, weaving or knitting is determined by, among others, the flexibility and friction characteristics of the material processed. In all these processes, a fibrous strand often comes into contact with a metallic surface or against another fibrous strand while it is moving at high speed. This action results in one of the following two consequences. It may increase the tension in the strand beyond the breaking strength of the strand, leading to breaking of the strand; or it may abrade the surface of the strand, leading to either breaking the strand or adversely affecting the quality of the strand and the resulting fabric. Hence, the friction and bending properties of the towpregs are identified as important properties of towpregs as far as textile processing is concerned.
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The very benefit of hybrid yarns of preimpregnated matrix material into the reinforcement material increases the bulkiness of the prepregs and the preform. Preforms with high bulk pose the following problems: ∑
Bulkier preforms make it difficult to produce good quality parts with complicated shapes, since they do not follow the contours truly. ∑ Preforms with high bulk need deeper mold cavities to make a part of the same thickness, compared to preforms with low bulk. ∑ It is difficult to predict and control the fiber orientation in a laminate made with bulky preforms. The mold halves have to move through a greater distance to consolidate these preforms. This brings about more disturbances in the fiber orientation. Hence, the lateral compressive properties of the prepregs are important as far as composite manufacturing is concerned.
12.3.3 Effect of raw material properties Studies carried out with a view to understanding the influence of raw material characteristics on the rigidity of the yarns and thereby on their processibility have been reported in the literature. The flexibility of finer filaments is better than that of the coarser filaments. In a study on air-jet texturing, Acar et al. [19] reported that yarns with finer filaments can be textured more satisfactorily than coarse filament yarns because they offer smaller bending and torsional stiffness and therefore a smaller drag force is necessary. Coarser filaments will require greater forces than the relatively finer filaments to overcome their inertial resistance. In a study on powder-coated prepregs, Ramasamy et al. [8] reported that nylon powder-coated towpregs had lower bending rigidity than PEEK powdercoated towpregs since the PEEK powder used was coarser. The cross-sections of filaments determine their area-dependent mechanical properties. Different cross-sections therefore need varying forces to deflect the filaments. Acar et al. [19] analyzed the effect of cross-sectional shape of filaments on loop formation. They observed that elliptical and hollow circular cross-sectional filaments texturize better than those with solid circular cross-section. Further they explained that non-circular and hollow filaments presenting a larger surface area than circular filaments of equal linear density are subjected to greater frictional drag forces relative to their inertias. Therefore, certain filament yarns with non-circular cross-sections are more suitable for improved air-jet texturing than yarns with circular cross-sections. Better blending of components and higher strength values of glass-nylon hybrid yarns was found when polyamide multifilament yarns characterized by a larger number of filaments of small linear density were used in pneumatic texturing [20].
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12.3.4 Effect of process parameters Hybrid yarns have reinforcing and matrix-forming filaments combined together in order to reduce the problems associated with the high melt viscosity of thermoplastic matrices. The easier will be the impregnation in subsequent consolidation of preforms if reinforcement filaments and matrix filaments are mixed well, ideally to the individual level. In this respect, the various techniques used to manufacture hybrid yarns produce the yarn structure typical of that process. Hence the level of mixing of the filaments of both reinforcing and matrix forming is greatly dependent on the process and the process parameters. The influence of these variables on the flexibility and compressibility of hybrid yarns is discussed below. Commingled yarns produced with air jet are very soft and drapable [21]. Torsion of the commingled yarns gives good cohesion in the yarn and facilitates further processing. The transverse compressibility of the commingled rovings composed of glass and polypropylene filaments was measured and compared with the respective transverse compressibility of a homogeneous polypropylene roving and a glass roving. The transverse compressibility of each homogeneous roving was fitted with existing equations developed by Gutowski [22] for aligned fibers. The model parameters of each of the two homogeneous rovings were then applied in series and parallel to reproduce the transverse compressibility of the commingled rovings. The configuration that applied the homogeneous polypropylene and glass rovings in series reproduced the best transverse compressibility of the commingled rovings studied. In wrap-spun hybrid yarns, increasing the wrap density increased the bending rigidity. The wrapping process brings individual filaments together and thus increases the structural integrity of the prepregs. Because of this action, the bending rigidity of the prepreg increases with increasing wrap density. Offerman et al. [23] compared commingled yarns developed under optimized conditions with friction-spun yarns. The variables used for the experiments include hybrid yarn take-up speed, air pressure and overfeeding rate of the glass roving. LD and Taslan nozzles were used for comparison and an LD-type nozzle was found to provide a high degree of interfilament mixing and homogeneity of component distribution. Manufactured commingled yarns were also compared with commercial GF–PP commingled Twintex yarns. The results showed that friction-spun hybrid yarns have 16% lower breaking strength than commingled yarn. Friction-spun yarn also showed significantly higher bending stiffness than commingled yarn due to its circular cross-section. The compression resilience of uncoated carbon yarn was found to be higher because of close packing of the filaments, while commingled yarn and powder-coated yarns were bulky.
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12.3.5 Preforming behavior The ability of hybrid yarns to be processed during preform manufacturing is one of their advantages over other types of prepreg manufacturing techniques, like powder coating, etc. The number of interruptions as a function of braider speed was used to determine the braidability of the prepregs during a certain time by Ramasamy et al. [8]. The authors found that commingled yarns were easier to braid than powder-coated yarns. Wrapping of thin nylon filament yarn can further enhance the braidability of commingled yarn. Powder-coated prepegs as well as commingled hybrid yarn prepregs showed a higher friction coefficient as compared to uncoated carbon fiber tows. The increase in the coefficient of friction is less in commingled tows than in powder-coated tows. Increasing the wrapping density in powder-coated tows had like effect on the frictional coefficient. This behavior indicates that greater care must be exercised to avoid problems like filament breakage and entanglements of neighboring threads. This aspect plays an especially important role in the case of the braiding process, due to the high level of the fiber-to-fiber friction.
12.3.6 Damage of reinforcing fibers during hybrid yarn manufacture Choi et al. [24] studied the effect of commingling with air jets on filament damage using Toray T300J carbon filaments and Hoechst PEEKM. They carried out the studies with different intermingling nozzles, namely Temco LD 32.04, 32.05 and 32.06, and the texturing nozzle was a DuPont Type XV 100/86D. The relative tensile strength (referred to the carbon filament fraction) and the yarn count were taken as measures of the degradation occurring to the carbon filaments. Figure 12.7 [24] shows the results of their studies with different nozzle types and air pressures. With all types of mingling nozzles there was a decrease in the relative strength and yarn count with decrease in the air pressure. This indicates that there is a reduction in the damage to the carbon filaments and loss of broken filaments with decrease in air pressure. Moreover, it can be observed from their results that the texturing nozzles lead to lower filament damage compared to that of the intermingling nozzles. However, the disadvantage of the gentle treatment of the carbon by the texturing nozzles is the unfavorable component distribution over the yarn cross-section. This is due to the differences in the working mechanisms of the air texturing and intermingling nozzles. Since the carbon filaments are highly sensitive to stresses acting perpendicular to their axis, the use of intermingling nozzles leads to greater filament damage. Offerman et al. [23] reported that glass fibers are difficult to handle during
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LD32.06 LD32.04 LD32.05 Type XV 100/86D
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580 560 540 520
LD32.06 LD32.04 LD32.05 Type XV 100/86D
500 0.35 0.4 0.45 0.5 0.55 0.6 0.65 Air pressure (MPa) (b)
12.7 Dependence of (a) yarn relative strength and (b) yarn count on air pressure and nozzle type.
textile processing due to their low bending and transverse compression strength. Improperly designed friction and deflection areas lead to filament damage and thus reduce the mechanical properties of the composite materials. Kruci´nska et al. [20] compared glass-nylon hybrid yarn structures made from ring twisting, friction spinning, air interlacing and pneumatic texturing. It was found that destruction of filaments during the twisting process was not as intensive as was found in friction spun yarns.
12.3.7 Fiber distribution in hybrid yarns The kind of technique used to manufacture hybrid yarns has a great bearing on the fiber distribution in the hybrid yarn. Lauke et al. [1] found through SEM observations that the homogeneity of the glass fiber distribution within the matrix is strongly dependent on the hybrid yarn structure. They ranked the hybrid yarns obtained from different techniques with respect to the average flow distance of the polymer which determined greatly the impregnation quality of the reinforcing fibers with matrix material. As per their findings, the flow distance increased in the order of Schappe yarn, commingled yarn, Kemafil yarn, side-by-side yarn and lastly friction spun yarn. This implies that Schappe and commingled hybrid yarns show the best degree of mixing of reinforcing and matrix fibers. Kruci n´ ska et al. [25] found the highest degree of fiber blending in the case of the textured and air-interlaced yarns, and the lowest in the case of the twist (ring twisted) and DREF technology.
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Manufacture of thermoplastic composites with hybrid yarns
The structure of thermoplastic composites is dependent on the application and the processing techniques used. Short-fiber reinforced and elastomer toughened thermoplastics are predominantly available in pellet or granule form for processing by injection or extrusion. For more demanding applications, long or continuous-fiber reinforcement is used in order to obtain the necessary mechanical properties. Pre-impregnated continuousfiber reinforced thermoplastics generally are in the form of a fabric where the thermoplastic resin is contained within the yarns themselves. The fabric can then be molded using various stamping or thermoforming methods, although because of the oriented nature of the fibers complex shapes are harder to process. The major manufacturing techniques of thermoplastic composites are presented below, including compression molding, filament winding, pultrusion, injection molding, the autoclave technique and diaphragm forming processes. This form of material is also available as a single yarn. Considerable property improvements can be obtained through proper selection of composite processing parameters.
12.4.1 Compression molding Compression molding of thermoplastic composites is a flow-forming process in which the heated composite sheet is squeezed between the mold halves to force resin and reinforcement fibers to fill the cavity. This is the only thermoplastic manufacturing process used in industry for making structural thermoplastic composite parts. The process is used for making bumper beams, dashboards, kneebolsters, and other automotive structural parts [26]. Glass mat thermoplastics are the major class of products manufactured from this technique. Another type of compression molding is the hot press technique in which intermediate thermoplastic materials like prepregs and hybrid yarns are used. In this process, thermoplastic intermediates are stacked together, placed between molds, and consolidated into composites by application of heat and pressure to melt the thermoplastic resin and impregnate the fibrous reinforcement [26]. The fiber volume fraction achieved by this process is greater than 60% and this process is most common in R & D to make flat laminates.
12.4.2 Filament winding Thermoplastic filament winding, also called tape winding, is a process in which a thermoplastic prepreg tape or hybrid yarn is wound over the
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mandrel, heat and pressure are applied at the contact point of the roller and the mandrel for melting, and consolidation of thermoplastics is effected. In this process, laydown, melting and consolidation are obtained in a single step, which thereby avoids the curing stage [26]. Thermoplastic tape is wound over the mandrel and various types of localized heating are used to melt the resin of the incoming tape at the consolidation point. During the process localized melting causes a high rate of heating and cooling, which requires different processing conditions from compression molding and autoclave processing. Three important parameters, heat intensity, tape speed or winding speed, and consolidation force, have a significant effect on the quality of the filament-wound part. Optimum process parameters for each heat supply and material type need to be determined to obtain a good consolidated part [26]. Higher capital investment, complexity of localized heating control and inferior quality of consolidated parts are major hindrances for popularization of this process.
12.4.3 Pultrusion process Among continuous methods of composite manufacture, pultrusion is an important process in which composites with precision cross-sections are prepared. Although thermosetting resins were favored for this method, recent trends towards utilization of thermoplastic matrices are being adopted with intermediate commingled yarns to facilitate impregnation. The intermediate hybrid yarn is fed from the spools through a preheating chamber into a forming die. The forming die consists of two sections, heating and cooling; thermoplastic matrix is melted in the heating section to achieve the impregnation. Subsequently resin-impregnated fibers are solidified by and formed into desired cross-sectional shapes in the cooling die. Because of the high viscosity of thermoplastic resins, processing becomes difficult and requires a higher pulling force. This process provides a surface quality inferior to that provided by thermoset pultrusion. Thermoplastic pultrusion has gained less interest from industry and academia.
12.4.4 Autoclave molding Autoclave molding is a process of thermoplastic composite manufacture in which the fibrous reinforcement and thermoplastic matrix are laid down on a tool in the desired sequence and spot welded to make sure that the stacked plies do not move relative to each other. The entire assembly is then vacuum bagged and placed inside an autoclave. Following the process cycle, the part is removed from the tool. Intermediate forms of thermoplastic composites between those from hybrid yarns and prepregs offer better processability in this technique. This process is similar to the hot press technique, the only
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difference being the method of applying pressure and heat. Composites for aerospace applications are the major products manufactured by this technique due to its versatile fiber orientation, higher fiber volume fraction, and quality of the material produced.
12.4.5 Inflation molding technique The bladder inflation molding technique, also known as the diaphragm forming process, is an economically competitive process for the production of thermoplastic composites with complex hollow parts, which overcomes some of the limitations of filament winding, rotomolding and pultrusion. The technique, as shown in Fig. 12.8, involves the placement of a composite preform around an expandable polymer mandrel, also known as a bladder. The composite–bladder assembly is then positioned in a mold and placed in a hot press. While the composite material is being heated, the bladder is inflated so as to conform the preform to the shape of the mold cavity. Once the thermal cycle is completed, the part is removed from the mold and the bladder is extracted, leaving a thin-walled hollow composite structure. This process, combined with the use of thermoplastic composite preforms, is currently used in the production of some tennis racquets and bicycle frames.
12.5
Compaction and consolidation of hybrid yarns
An important step during the molding of thermoplastic composites is to apply an external load transverse to the composite plane. The induced pressure is intended to squeeze air and resin out, to suppress voids and to increase and make the fiber volume fraction uniform. In addition, the applied load in concert with the tool and surface materials will establish the dimensions and the surface finish of the part. This compaction process is called consolidation and plays a critical role in deciding the mechanical properties of the composite. The compaction of the bundles results in a steadily increasing internal
Heating element
Reinforcing fiber
Thermoplastic fiber
Commingled yarn
Tubular braid
Mold P
Commingled yarn braid Bladder tube
Bladder inflation molding
12.8 Steps in bladder inflation molding.
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pressure. As the applied pressure increases, the reinforcement fibers start to move towards each other. After melting, the matrix fibers or droplets sustain the hydrostatic pressure and thus oppose the further displacement of the reinforcement fibers. The matrix polymer will yield when a certain threshold of pressure is exceeded. Eventually the applied pressure drives the matrix into the spaces between the reinforcement fibers while reducing the voids until the bundle is completely impregnated. The time to reach full consolidation depends on the time taken to fully impregnate the reinforcing fiber bundles. It is desirable to minimize the time to consolidate so as to maximize the rate at which the process may be repeated. The time to consolidate is dependent upon the material properties and the consolidation process parameters. The process parameters include maximum applied pressure, rate of pressure application, temperature and time. The structure of the fabric, yarn dimension and shape, number of fibers per yarn, fiber diameters and the quality of mixing of reinforcing and matrix fibers in the hybrid yarn bundle affect the rate at which matrix impregnation and fiber wetting occur and therefore influence the time to consolidate. Van West et al. [27] have studied the physical process of consolidation in the case of commingled thermoplastic composites. Due to the differences in distribution of matrix and reinforcing fibers in the preform, the consolidation process was found to be different for commingled fabric from that of a layered prepreg. In this experiment, several layers of commingled fabric were subjected to pressure at the melt temperature in a tapered mold. At one end of the mold, the fabric experienced full consolidation pressure and at the other end it experienced zero pressure. From the micrographs, at the zero pressure end of the specimen, yarns were seen in cross-section to be well separated from one another containing dry reinforcing fibers with attached pools of matrix. With the increase in pressure, the bundles moved closer together so that matrix bridging occurs between them. When the applied pressure was sufficient, the individual matrix pools coalesce, surrounding the dry fiber bundles. Further increase in pressure drove the matrix into reinforcing fiber bundles, reducing voids within the bundles until the yarns were completely impregnated and full consolidation could take place. During the consolidation stage, three main mechanisms take place. These are: ∑ Intimate yarn contact by compression ∑ Autohesion ∑ Fiber bundle impregnation. Out of these three mechanisms, fiber bundle impregnation is the leading one. Philips et al. [28] studied consolidation of CF/polyetherimide and found that intimate contact and autohesion processes consumed only 1% of the total consolidation time.
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12.5.1 Fiber–matrix adhesion On the application of load, it is the matrix which takes up the load and is supposed to transfer it to the embedded fibers. Ideally the fiber–matrix bond must be perfect, i.e. presenting the same properties as that of the matrix, since it is the weakest constituent. A strong fiber–matrix bond is desirable to improve interlaminar shear strength, delamination resistance, fatigue properties and corrosion resistance. However, in some cases a weak bond may be preferable since the damage tolerance of the composite with a brittle matrix usually is enhanced by a weak fiber–matrix bond. This means that whatever is the load case, the fiber–matrix interface is of crucial importance to the properties of the composite. Due to such great significance of the aspect of fiber–matrix adhesion, much effort has been made in understanding and improving the interface between fiber and matrix. Saiello et al. [29], while studying the relationship between fiber–matrix interactions with matrix crystalline morphology in the case of carbon/PEEK composites, reported that the crystalline content determines the fiber–matrix adhesion. The crystalline content was varied by different thermal treatments. The amorphous matrix composite with less than 5% crystallinity showed a fracture characterized by the presence of clean fibers protruding from the matrix. There was no resin on the fiber surface or where fibers had been pulled out from the matrix. This indicates poor fiber–matrix adhesion. When the same amorphous matrix composite was crystallized by cooling the melt and keeping the composite at 320°C, the material behaved like the semicrystalline matrix composite. The presence of a crystalline phase is evident and the fibers are still covered by the matrix after the fracture. This indicates better fiber–matrix adhesion. For many composite systems, the presence of fibers has been shown experimentally to influence the crystallization kinetics of the matrix polymer. Mehl and Rebenfeld [30] have reported the simulation of crystallization kinetics and morphology in fiber reinforced thermoplastic composites in twodimensional and three-dimensional cases. The addition of fibers to a given crystallizing system increases the complexity of the system by adding fiber surface which can both constrain growth by an impingement mechanism and enhance crystallization by adding fiber nuclei. The constraining effect is relatively small at low fiber fraction, but increases rapidly with fiber content. The regions of oriented spherulites referred to as the transcrystalline region occur near the fiber surfaces when local fiber nucleation density is so large that spherulites are constrained by their neighbors to grow in a direction perpendicular to the fiber axis. An increase in bulk nucleation density will suppress the extent of the transcrystalline region, while an increase in fiber nucleation density will enhance it. Increasing fiber content does not always depress the rate of crystallization. The effects of increase in fiber content on
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crystallization for a system with a fiber nucleation density of 800 nuclei/cm showed an enhancement of the crystallization rate. This is because the additional fiber nuclei from the larger fiber surface overcompensate for the depression in kinetics due to increased impingement. Larger-diameter fibers are less effective than small-diameter fibers in depressing crystallization by constraining growth and in enhancing crystallization by providing fiber nuclei. This is due to the fact that it is the surface of the fibers that controls both the constraint of growth and the number of additional fiber nuclei added to the system, and fiber surface per unit area decreases with increasing fiber diameter.
12.5.2 Consolidation quality Consolidation quality is an essential factor during manufacture of thermoplastic composites since it has a significant bearing on the mechanical properties of the composites. Void content is the most indicative factor for consolidation quality of the composites. Ye et al. [3] used density measurements to correlate the consolidation state with the apparent void contents in composites. From the effect of Dcom, i.e. degree of commingling, on consolidation quality as seen in Fig. 12.9, it was observed that the higher the value of Dcom, the faster is the consolidation of the composite. These results confirmed that the commingling state has a strong effect on the impregnation process and the resulting consolidation quality. Producing a high commingling state of the material preform and maintaining this status during transportation of the preform may improve the impregnation behavior and consolidation quality in the subsequent manufacture of composite parts. Figure 12.10 illustrates the consolidation quality of CF/PEEK composites 40
Xv (%)
30 Dcom Dcom Dcom Dcom
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10
0
0
10
t (min)
= = = =
0, T = 400°C 75%, T = 400°C 0, T = 380°C 75%, T = 380°C
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12.9 Consolidation qualities evaluated by fully unmingled and partially commingled model [3].
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T = 380°C T = 400°C T = 420°C
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12.10 Consolidation quality of CF/PEEK composites as a function of holding time at different processing conditions [3].
as a function of holding time in different processing conditions [3]. The symbols indicate the experimentally measured apparent void contents. The solid lines indicate the predictions from the model at Dcom = 75%. It can be seen that both applied pressure and holding time greatly affected the quality of consolidation. An increase in either holding time or applied pressure obviously reduced the void content in the composites, and gave better consolidated materials. Figure 12.10 also shows that in spite of good distribution of the reinforcing and the polymer fibers in the commingled yarn (in the non-molten state), the observed unmingling step at the onset of melting of the polymer fibers and the high viscosity of the matrix (at the temperature studied 380°C, the matrix viscosity is 591 Pa s) at low processing temperature still obstruct fast consolidation and the achievement of void-free composites. But from Fig. 12.10 it is clear that the material reached a fully consolidated status when the holding time was about 20 min at pa = 1.5 MPa and T = 420°C (at this temperature the matrix viscosity is reduced to 109 Pa s). These findings endorse a good correlation between experimental results and predictions from the consolidation model at Dcom = 75%. Sakaguchi et al. [17] compared commingled yarn composites with uncommingled and film-stacking composites for studying the influence of impregnation quality on the mechanical properties of composites. They found that at lower compaction times, uncommingled and film-stacking composites showed poor bending strength, which is an indicator of poor impregnation quality, whereas the commingled yarn composites showed better bending strength at the same parameters, indicating that the impregnation is better in these composites made from commingled yarns. Further it was noted that with increase in the compaction time, the bending strength increased, thereby indicating further improvement in impregnation quality.
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12.5.3 Effect of molding parameters on the microstructure and mechanical properties It has been mentioned in a comparison between the merits and demerits of thermoplastic and thermoset composites that short processing time is an advantage offered by thermoplastics over thermoset composites because such shorter time provides flexibility in adapting various manufacturing technologies to improve production efficiency. However, the recommended processing conditions, like temperature and pressure, in the case of carbon/ PEEK composites, for example, are 380°C and 1.4 MPa, respectively. These are much higher than those required for thermoset composite manufacturing for, e.g., epoxy-based composites. This makes it difficult to make use of cost-effective manufacturing technologies for fabricating components from carbon fibers/PEEK composites. Much research has been carried out in studying the processing conditions vis-à-vis composites performance to search for opportunities in broadening the processing window for the composite. The influence of these parameters on the quality of composite is reviewed in this section. Mechanical properties are greatly dependent upon the molding conditions. It was found that GIC,init, i.e. mode I fracture energy release rate, is most sensitive to the molding conditions. Each of the molding parameters discussed below has a bearing on the quality of consolidation that can be achieved and thereby in turn on the mechanical properties. The following section compiles various studies conducted so far on this aspect of composites manufacturing. The preheat temperature has a significant effect on the quality of the thermoplastic composite manufactured, which can be seen in the studies conducted on the glass/PP commingled hybrid yarn composites wherein increase of preheat temperatures resulted in higher strength and stiffness coupled with reduction in void % in the laminates [30]. Compaction time Ye et al. [3] studied the consolidation quality of commingled CF/PEEK composites. It was stated that at a given temperature and pressure, an increase in compaction time reduces the void content in the composites, indicating improvement in the quality of consolidation with time. A study carried out by the same authors on the mechanical properties vis-à-vis void content had shown that with increase in the void content, the mechanical properties, like ultimate strength and transverse elastic constant, deteriorated. It can be inferred from these findings that an increase in compaction time improves the mechanical properties of composites. With the increase in the use of 3D composites for high performance applications, this parameter has gained further significance. Compaction time is more critical for 3D composites that need a longer time for heat transfer [31]. © Woodhead Publishing Limited, 2010
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Tool temperature This parameter affects the mechanical properties through void content. A low temperature can suppress the flow of resin and lead to poor fiber wetout. A higher temperature favors fiber impregnation. However, an excessive temperature can degrade the resin and the composite. An optimum molding temperature depends not only on the resin but also on reinforcing fiber and their configuration. For thick 3D composites, a lower resin viscosity is especially needed because the complex fiber configuration can hinder the flow of resin. Hence, it will require a higher processing temperature. It was reported that with increase in temperature, the void content and in turn the mechanical properties of composites from CF/PEEK commingled hybrid yarns improved [3]. Kuo and Fang [31] reported that in the case of 3D orthogonally woven and two-step braided thermoplastic composites, a higher mold temperature results in a higher flexural modulus for specimens of the same thickness. The improvement in the flexural modulus is more prominent in thicker specimens than in thinner specimens. This could be explained by the fact that enhancing the bonding of an already adequately bonded composite as in the case of thinner composites will not improve its modulus. Fiber content is the sole factor governing the modulus. On the other hand, for those weakly bonded, as in the case of the thicker composites, improving the bonding through temperature increase apparently benefits the modulus. Effect of pressure As in the case of temperature discussed above, pressure also affects the mechanical properties through void content. With the increase in pressure, the void content and thereby the mechanical properties of the composites made from CF/PEEK commingled yarns improved [3]. This was found that the flexural modulus drops sharply as the thickness increases [31]. This can be explained by the fact that the modulus is proportional to the fiber volume fraction along the axial direction. As the thickness increases the axial fiber content drops. The molten resin is insufficient to fill inter-yarn and intra-yarn spaces, thus leading to a weak bonding in thicker specimens which hence showed more drop in reduction in flexural modulus than thinner specimens. Flexural strength also showed the same changes as flexural modulus with the change in thickness.
12.6
hybrid yarn structure – composite property relations
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consolidation. Hence it plays a critical role in the final composite properties such as void content and fiber matrix distribution. The orientation and its distribution of reinforcing fibers along the yarn axis decide the modulus and other mechanical properties.
12.6.1 Voids and their distribution In the manufacture of composites, voids have a big role to play, so much so that the consolidation quality was evaluated by means of void content 125. Micrographs of polished areas of composites made with the different hybrid yarns are shown in Fig. 12.11 [1]. The process parameters during consolidation have a great effect on the void content and thereby the quality of the composite. In such an experiment, Klinkmuller et al. [32] found in GF/PP laminates that an increase in pressure from atmospheric level to 0.375 MPa gave a large reduction in the void content. However, a further increase in pressure or holding time did not reduce the number of voids in the laminate. A temperature increase up to 175°C resulted in a large void
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12.11 Micrographs of polished section of composite laminates made from (a) side-by-side yarn, (b) Kemafil yarn, (c) commingled yarn, (d) friction spun yarn [1].
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reduction whereas a further increase did not have a major influence on the void content. In another study, Ramasamy et al. [33] examined voids in laminates made from braided preforms out of powder-coated and commingled tows of carbon fiber/Nylon 6. The preforms were braided into ±45° biaxial fabrics and then consolidated. Temperature, pressure and time were varied, keeping the cooling rate at 5°C/min. Two kinds of voids were observed in the laminates. Voids in the yarn had a size of about 12–20 mm, while voids between the yarns were of the order of 80–120 mm. At 260°C, the void content for the powder-coated laminates varied from 0.8–5.4% whereas for the commingled laminates it varied from 2.8–5.3%. This suggested that the resin placement with respect to the carbon fibers is well dispersed in the powder coated tows compared with the commingled tows. Analysis of variance (ANOVA) carried out on the void content data revealed that the main effects of consolidation temperature and pressure were significant at the 99% confidence level, whereas consolidation time had an insignificant effect on void content and it was found that resin flow for consolidation had happened in less than 5 min. In yet another study, Svensson et al. [21] examined laminates made from commingled and co-wrapped yarns using aramid, carbon and glass fibers as reinforcements and spun polyamide and polyimide as matrix. They found that the laminates manufactured from the co-wrapped yarns contained voids and resin-rich pockets, whereas commingled laminates showed very good impregnation and distribution of reinforcing fibers.
12.6.2 Fiber distribution Homogeneity of glass fiber distribution within the matrix is strongly dependent on the hybrid yarn structure [1]. In the family of hybrid yarns manufactured by various techniques, the SCH and COM composites show the best degree of mixing of reinforcing and matrix fibers. The degree of mixing of reinforcing and matrix fibers in the hybrid yarn has a considerable bearing on the consolidation quality of the composite and the reinforcing fiber distribution in the composite. Impregnation of the reinforcing fibers with matrix material is determined mainly by the average flow distance of the polymer, a parameter difficult to express quantitatively but which depends on the degree of mixing. The yarns may be ranked according to increasing flow distance as follows: SCH, COM, KEM, SBS and FS. Consequently one can expect that the impregnation quality of the glass fibers with polyamide matrix for the yarn structures investigated will be the highest for SCH composites and decrease towards FS composites. Another parameter is the possibility of fiber flow, i.e. the fibers themselves can move together with the matrix. In compression molding of a flat plate,
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this movement is negligible for continuous yarns, which can be considered to be fixed. The Schappe yarn consists of discontinuous fibers and thus such movements are possible. If all of these parameters are compared, the Schappe and COM yarns come out the best, followed by SBS, then KEM, and the worst material is the FS.
12.6.3 Mechanical properties Composites are finding widespread usage in various applications over their traditional counterparts like metals, ceramic, etc., for their mechanical properties, mainly their comparatively high strength to weight ratio. In fiber reinforced composites, reinforced fibers are the main load-bearing components in the composite system. Hence the mechanical properties are very much dependent on the orientation, distribution and form of the reinforcing fibers in the composite. For example, commingled spun yarns produced by Schappe technology, which consist of the reinforcing fibers in the staple form, will have a certain degree of disorientation due to the yarn’s twist and hence will never reach the mechanical properties offered by continuous fiber reinforced composites [34]. Similarly, a cover core structure produced through the friction spinning method will comprise thermoplastic matrix staple fibers wrapped around reinforcing filament yarn core. Due to the core/sheath structure, mixture of the reinforcing fibers and matrix fibers will be poor. In yet another study, Kruci n´ ska et al. [25] reported that the mechanical properties of composites manufactured for hybrid yarns depend on the degree of component blending in the hybrid yarns, and on the level of weakening of glass filaments resulting from the process of component linking. Tensile properties In a comparative study conducted by Li et al. [34] on compression molded unidirectional composites made by UY1 (side-by-side laying of glass fibers and polypropylene) and UY2 (side-by-side laying of bulked glass fibers and polypropylene) vis-à-vis AJCY (air-jet commingled yarn), it was found that the transverse bending properties of UY1 composites, especially the bending strength, are lowest. This is because the mixing of glass fibers/polypropylene filaments and the bulkiness of glass fiber roving is the poorest. Therefore, when the polypropylene filaments are melted into the matrix, the impregnating property of UY1 is inferior to those of UY2 and AJCY composites. The bending properties of UY2 composites are superior to those of UY1 composites because of the appropriate bulkiness of glass fiber roving. Owing to the better mixing of glass fibers and polypropylene filaments in AJCY, the bending properties of these composites are highest. With the increase in bulkiness of glass fiber roving, the velocity of the matrix impregnating
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fibers increases, resulting in good cohesion between fiber and matrix. So, the bending strength and bending modulus of composites made from commingled yarns increase with the increase in bulkiness of glass fiber roving. After a single yarn is compressed at high temperature it was observed for a single UY1 that there was little polypropylene among the glass fibers; but more around glass fiber roving. For a single AJCY, however, there is lot of polypropylene among the fibers. So, the mixing of glass fibers and polypropylene elements can increase the velocity of polypropylene-impregnated glass fibers. Hence the bending properties were found to be better in the case of AJCY than for UY1 and UY2. Kruci n´ ska et al. [25] have reported that in the case of compression molded composites made from flat knitted fabrics of hybrid yarns spun by various techniques such as twisting, friction spinning, air interlacing and air texturing, the highest values of tensile tension and bending tension were obtained for the composite produced from a modified multi-segment yarn produced by the air-jet textured method, which is characterized by the highest degree of blending of both types of fiber. Lauke et al. [1] discussed the influence of hybrid yarn structure on the composite tensile properties. Besides fiber strength, the strength of fiber reinforced composites depends upon the fiber volume fraction and fiber orientation, and the existence of fiber ends (discontinuous fiber reinforcement) is a very important factor. It leads to local stress concentrations that may cause matrix, interface or fiber fracture. Lauke et al. ranked the hybrid yarns with decrease in tensile longitudinal strength as SBS, FS, KEM, COM and SCH. The fiber volume fraction in SBS was 0.46 whereas in SCH it was 0.56. By the rule of mixtures, the strength of SCH composites should have been higher by around 20% than that of the SBS yarns. However, experimental results showed the opposite. This behavior is mainly clarified by the arrangement of reinforcing fibers in the composites. The possibility of flow of the discontinuous fibers in the SCH material can result in different fiber orientations, and the fibers in the commingled yarn are waved, whereas the fibers in the other variants have a more or less unidirectional (UD) orientation. Longitudinal tensile modulus also showed the same trend as that of longitudinal tensile strength. Transverse strength and transverse modulus depend strongly on the composite microstructure, especially on the homogeneity of the distribution of reinforcing fibers, on their directionality and impregnation quality, the latter being dependent on wettability and quality of the fiber–matrix adhesion. The SCH and COM yarn structures result in composites with the highest values for transverse strength and modulus. As discussed above, these two hybrid yarns contain discontinuous fibers or disoriented fibers, respectively. This fact results in the notably better transverse properties compared with the other yarn structures. The FS yarn is constructed by parallel bundles of glass fibers surrounded by
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matrix filaments, and the flow distances are the highest, resulting in a bad impregnation quality and consequently in the worst transverse properties. Impact properties Composite materials outperform traditionally used materials like metals in some critical applications such as aircraft due to their high strength to weight ratio, better stiffness, lower cost and time to manufacture components. However, these materials do suffer some serious limitations. The most significant amongst these is their response to localized impact loading such as that imparted by a dropped tool or runway debris. The manner in which the composite materials respond to impact loading and dissipate the incident kinetic energy of the projectile is very different from that of the metals. Unlike in metals which absorb the energy through elastic and plastic deformation, composites have very limited ability to undergo plastic deformation, with the result that energy is frequently absorbed in creating large areas of fracture with significant reduction in strength and stiffness. Since high performance composites made from continuous fibers are being used increasingly in the design of a large number of civil and military aircraft wherein the consequences of impact are most serious, research has been undertaken to study the impact response of these materials. The impact response of fiber reinforced composite is dependent upon its constituents, i.e. fiber, matrix and interphase responsible for assuring the bond between matrix and fiber. It is in the impact response where thermoplastic composites surpass thermoset composites. It has been reported that the energy required for fracture of thermoplastic composites is greater than that of thermoset composites. The impact resistance of composite materials also depends upon the specific order in which the plies are stacked [35]. Unidirectional composites, having all their fibers aligned in one direction, fail by splitting at very low energies and are therefore highly unsuitable for applications where impact loading might occur. Composites having ±45° surface plies offered superior impact resistance and improve residual strengths. It was suggested that ±45° plies increased the flexibility of the composite, thereby improving its ability to absorb energy elasticity. Stevanovic et al. [35] have found that ±45° composites were capable of absorbing considerably more energy than (0°, 90°), (0°, +/45°) and (0°, 90°, +/45°) laminates. Impact-induced delamination can be reduced by the use of woven fabrics, hybridization (for example, carbon fibers with linear fibers) and threedimensional stitching. The three-dimensional nature of the fabric helps to suppress the formation of delaminated zones at the critical interface. Su [36] conducted mode-I delamination tests on both stitched and non-stitched AS4 carbon fiber/J1 (a semi-crystalline thermoplastic) and it was found that stitching with Kevlar® fiber resulted in a 100% increase in inter-laminar
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fracture toughness. Instrumented drop weight impact tests on a number of 2D and 3D composites indicated that the latter offered a superior impact resistance, once the presence of the third dimension reinforcement served to inhibit the propagation of delaminated zones. Yet another study [37] showed that stitching carbon fiber composites improves the residual strength following impact. It has also been reported that the residual strengths of mixed woven composites were superior to that of the standard material manufacturer from unidirectional plies. Fatigue and interlaminar fracture In a study of hybrid yarn composite property relationships [25], it was confirmed that the interphase properties, like interlaminar shear strength, depend on the level of blending of reinforcing fibers and thermoplastic fibers in the source material used for the production of composites. In the case of DREF yarn and twisted yarn, in which fibers form clusters, the interlaminar shear tension values were found to be low. Good component blending in air-interlaced yarns and in pneumatically textured yarns showed a positive influence upon resistance to shearing of the composites. Further improvement in the blending of both components that was obtained for textured yarn, the so-called ‘multi-segment’, contributed to a considerable growth of interlaminar shear strength from 22 MPa to 30 MPa. Diao et al. [38] found that unidirectional CF/PEEK commingled composites exhibit quicker degradation than APC-1 (carbon fiber reinforced PEEK) in a fatigue test, indicating that the commingled composites are more fatigue sensitive. Gilchrist et al. [39] studied the interlaminar fracture of commingled glass fiber/PET composite laminates for woven and warp-knitted structures. They reported occurrence of crack propagation in a combination of three modes: tensile opening or Mode I, sliding shear or Mode II, and tearing shear or Mode III. They found that in Mode I interlaminar fracture, which was investigated using a DCB test, the fracture toughness of the warp-knitted laminates was only slightly lower than that of the woven laminates; this was attributed to the weft yarns which effectively prevented crack propagation in the woven laminates. This conclusion presents good agreement with the work of Yoon and Takahashi [40] on Mode I interlaminar fracture of CF/PEEK composites. These authors reported that the cracks were arrested by the weft yarns and that a higher stress was needed to reinitiate the cracks. Svensson et al. [41] saw no difference between the fracture behavior of the woven and the warp-knitted laminates, and the load-displacement curves were non-linear before the maximum load was reached. In Mode I failure the most dominant surface characteristic was fiber pull-out. A large amount of fiber pull-out was seen in SEM photographs of the fractured composites. In woven laminates,
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the weft yarns prevented extensive pull-out of the fibers and yarns in the warp direction. In Mode II fracture tests, the authors had seen that crack propagation was more stable than in the Mode I type. As in Mode I, in Mode II tests also the warp-knitted laminates showed marginally lower fracture toughness than the woven laminates. The authors reported the formation of cusps, which were reported in other literature as a stacked lamellar structure and serrations, as the most important feature of matrix fracture in this Mode II fracture. The higher fracture toughness of thermoplastic composites than for thermoset composites was attributed partly to processes such as extensive fiber pull-out caused by a poor fiber–matrix interface and fiber misalignment, the presence of large resin pockets, and in Mode II dominated failures, the deformation of the matrix and the formation of cusps. The decrease in interlaminar and intralaminar shear strengths followed the increase in fiber alignment and/or the increase in flow distance, and was ranked by Lauke et al. [1] as SCH, COM, (SBS, KEM), FS. The highest Mode I critical energy release rates, as well as Mode II values, for crack initiation with the DCB, SEN and ENF tests were found for the laminate made with COM yarns. Also the COM composites show the highest crack propagation resistance. This result was explained by the fact that the main contribution to the energy-dissipation process is fiber bridging related to debonding and subsequent fiber fracture, as observed by an optical microscope during the test. As the crack was propagating, misoriented fibers debonded from the matrix but remain attached to the material on both sides of the crack and thus caused fiber bridging. This leads to a higher crack resistance compared with composites without this energy-dissipation mechanism. The SCH material also shows this mechanism but the peel-off lengths were found to be limited by the fiber length. In the case of the KEM and FS composites, the delamination crack was found to be propagating through the fiber bundles and through matrix-rich zones. It was found by Ferreira et al. [42] that the fatigue strength is strongly influenced by the layer design. Their analysis showed that the fatigue strength of 0° laminates (where the fiber direction is always the same as the load) is much higher (1.5 – 1.8 times) than for the other two laminates. This effect is related to the change of failure mechanism. In +45°/0°/–45° and +30°/–30°/0° laminates the predominant fatigue mechanism is the debonding between the fibers and the matrix caused by normal stresses. The fatigue strength obtained in +30°/–30°/0° laminates is 10 –15% lower than in +45°/0°/–45° laminates, which is a consequence of the higher normal stress component in the fibers with 30° of inclination. The failure is observed in inclined planes along the fiber direction. In 0° laminate the normal stress is predominantly absorbed by longitudinal fibers and the failure is in transverse planes.
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Potential application areas of thermoplastic composites
The advantages of thermoplastic composites over thermoset composites have already been discussed in Section 12.2. As a result there is growing interest in applying thermoplastic composites over a much wider area than had been envisioned earlier, including in areas such as sports and automotives. The ranges of applications for which thermoplastic composites are being considered are discussed below.
12.7.1 Aircraft applications Examples of applications of thermoplastic composites in aircraft are access panels and doors, engine cowlings, movable wing surfaces such as elevators, rudders, flaps and ailerons and spoilers. Aircraft floor panels are made through thermofolding wherein the laminate is locally heated and folded. This process gives durable products at low cost in such applications. The ice protection plate of Dornier 328 is a continuous fiber reinforced aramid/PEI plate. It protects the aircraft fuselage from ice thrown off the propellers. All four plate edges are thermofolded in quick consecutive processing cycles. The folded flange is only 6 mm wide and provides a fairing between the plate and the aircraft fuselage skin. It features folded sandwich panel edges to act as reinforcement and to keep condensing water from running over the edge. Thermofolded panels for a toilet module of the new Fokker 60 were developed and manufactured. Press-formed thermoplastic ribs have been in production for the Dornier 328 turboprop flaps. A carbon/PEI prepreg was used extensively in these applications. Press-formed edge members form an integral part of the primary structure floor panels found in the area over the wing. The floor panels act as a pressure bulkhead and connect the fuselage halves. Therefore, these heavily loaded panels are considered a primary structure. The C-shaped sections are located along the edges of the boards and serve to transmit high loads. The sections are press-formed by the same process as the Dornier 328 ribs.
12.7.2 Industrial applications Choi et al. [43] used carbon fiber–PEEK commingling hybrid yarns to manufacture lightweight high-performance rotors in complex applications. Hexcel claims that its products Towflex PPS, PEI and PEEK are suitable in various applications in industrial and medical components requiring high operating temperatures, wear resistance, resistance to corrosive chemicals and low thermal expansion. For example, it is claimed that vacuum pump vanes will benefit from increased operating efficiency over a wide temperature
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range due to the material’s very low thermal expansion. Another example quoted was the bushings and seals used in oil drilling operations and chemical refineries where resistance to wear and loads at high temperatures in corrosive fluids can increase their service life. These are also claimed to be suited for semiconductor manufacturing equipment components wherein the properties like dimensional stability, chemical resistance and wear resistance are beneficial. Bicycle frames can also be manufactured from thermoplastic composites. Mallick [44] of ABB corporate research, Switzerland, worked on using thermoplastic composites in high performance turbo-machinery components. The mechanical vapor compression (MVR) process is used in the evaporation of dairy and food products such as milk powder, soymilk, sugar, fruit juices and herbal extracts. This process relies on a high speed centrifugal compressor. As an alternative to these precision machines with high investment and maintenance costs, high pressure fans have been developed by ABB. Such fans rely on a simpler centrifugal impeller. The modern impeller speeds, at 270 m/s, are close to the material limits of metals. Being lighter in weight, fiber reinforced polymeric composites can fulfill these requirements. The various subcomponents like the blade, inlet plate, back plate and front plate are made out of composite materials. The cost of such impellers was shown to be much lower than for those made of steel. In industrial motors, thermoplastic composites are used. In the rotor windings of electrical machines, at the end of the rotor, the conductor windings overhang to accommodate the turns. This overhang is supported against centrifugal loads by retaining rings. These rings are sometimes made of glass/polyester composite material which has shown great advantages over steel rings.
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trends in thermoplastic composite applications
12.8.1 Natural fiber reinforced thermoplastic composites The preservation of natural resources and recycling has led to a renewed interest concerning natural materials with the focus on renewable raw materials. Natural fibers can be advantageously utilized for the development of recyclable or biologically degradable composites with good physical properties; in fact they are observed to be suitable for reinforcements with thermoplastics due to their relatively high strength, stiffness and low density. Natural fiber reinforced thermoplastics have good potential as a substitute for wood-based material in many applications. The development of environmentally friendly green materials owes much to natural fiber’s biodegradability, light weight, low cost, ease of recycling and use of renewable natural sources. The
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physical properties of natural fibers are mainly determined by their chemical and physical composition, such as the structure of the fibers, chemical content, angle of fibrils, cross-section, and degree of polymerization. Only a few characteristic values, but especially the specific mechanical properties, can reach comparable values of traditional reinforcing fibers. Collective thoughts through reviews on natural fiber reinforced composites and cellulose fiber reinforced composites by Bledzki and Gassan [45] have pondered upon these positive aspects as well as critically discussing the shortcomings and ways to improvise the interface bonding. Several natural fiber composites are reported to have nearly achieved the mechanical properties of glass-fiber composites, and they are already being applied, e.g. in the automobile and furniture industries, the most important natural reinforcing fibers being jute, flax and coir. Jute reinforced thermoplastic composites are the most commercialized materials among the natural fiber reinforced thermoplastic composites. Intermediate yarn with jute axial reinforcement along with PP and polylactic acid polymer braided around it was wound on a drum and hot-compacted to prepare thermoplastic composite. Jute-based composites, an alternative to wood products, are not severely affected by mites or moisture, and are generally considered to be fire-retardant and chemical-proof. Jute-based green composites would be suitable even for primary structural applications such as indoor elements in housing, temporary outdoor applications such as low-cost housing for defense, and rehabilitation and transportation. Due to its insulating characteristics, jute may find areas of applications in automotive door/ceiling panels and panels separating the engine and passenger compartments. Such panels made from jute fibers and PP/ bio-thermoplastic and hybrid composites are already in use. Fiber type, textile architecture, interphase properties, fiber mechanical properties and content were found to strongly affect the fatigue behavior of flax and jute fiber reinforced PP composites. The properties of sisal fiber, the interface between sisal fiber and matrix, the properties of sisal reinforced composites and their hybrid composites have been reviewed, and it has been pointed out that the mechanical and physical properties of sisal reinforced composites are very sensitive to processing methods, fiber length, orientation and volume fraction. Further, sisal and glass fiber hybrid composites have been observed to have better mechanical properties with hybridization. Mechanical and fracture behavior of a sisal–LDPE thermoplastic composite with respect to interfacial adhesion has been studied, and it was inferred that the better reinforcing effect was due to the high matrix ductility along with the high strength/modulus ratio. Flax has been tried by many researchers to reinforce thermoplastic matrix to manufacture composites; similarly, other natural fibers such as pineapple, kenaf, keratin and coconut have been tried and successfully reinforced with
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thermoplastic resins such as polyethylene and polypropylene (PP) to prepare recyclable thermoplastic composites. The disadvantages associated with natural fiber reinforced composites are moisture uptake, quality variations and low thermal stability. Based on investigations on the potential of natural fibers as reinforcements for composites, in several cases the results have shown that natural fiber composites have good stiffness but the composites do not reach the same level of strength as glass fiber composites. In comparison to conventional high performance reinforcement fibers, the lower thermal stability of natural fibers up to 230°C limits the number of thermoplastics to be considered as matrix material for natural fiber thermoplastic composites. Only those thermoplastics whose processing temperature does not exceed 230°C are usable for natural fiber reinforced composites. These are, most of all, polyolefines, like polyethylene and polypropylene. Technical thermoplastics, like polyamides, polyesters and polycarbonates, require processing temperatures of 250°C and are therefore not usable for such composite processing without fiber degradation [45]. Along with natural fiber reinforcements, many researchers have pondered upon the concept of totally biodegradable composite materials by trying biopolymers as matrix for such fibers. Major matrices for biodegradability include polylactic acid (PLA), polycaprolactone (PCL), soy-oil based epoxy, starch, polyhydroxybutyrate (PHB), modified cellulose and polyester amide. Among these, natural fiber reinforced thermoplastic PLA composite offers all the advantages of composite materials with respect to mechanical properties coupled with biodegradability. Polylactic acid polymers or polylactides are polyesters of lactic acid, and these polymers have recently been introduced commercially for products where biodegradability is desired. Studies on flax-PLA compared with flax-PP thermoplastic composites show satisfactory mechanical properties of flax-PLA composite with 50% better compression strength compared to flax-PP composites.
12.8.2 Environmental issues and recyclability These synthetic fiber reinforced composites are neither easily recyclable nor biodegradable, hence making disposal of these composite scraps an uphill task. The world community is getting more and more concerned about the ecological imbalance created by these materials with respect to the economics of using composites vis-à-vis the cost to be incurred on their recycling, reuse or disposal. Steps are being taken with legislation to ensure that the imbalance is minimized, so that a long considered advantageous area of composites for recycling, i.e. thermoplastic composites, is no longer favored over thermoset composites. DuPont’s Composite Recycle Technology [46] is a closed loop polyamide recycling process which converts parts made of glass or mineral filled polyamide
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6 or 66 into first-use quality material. The process involves dissolving used polyamide and then filtering away contaminants and fillers. The molecular weight of the recovered polyamide is increased to the level required for the final application. The process is claimed to generate resin that is equivalent to virgin polyamide resin. In another study conducted by Zafeiropoulos et al. [47], low density polyethylene matrix material remaining on short glass fibers after recycling was examined by SEM, DSC and TGA. It was found that on subsequent use of such recovers, short glass fibers with fresh polyethylene, polymer remnants and the new matrix can recrystallize, after applying shear stress to the melt, to form a trans-crystalline layer around the fiber, thereby making recycling of such composites feasible. In an effort to characterize products made from recycling of glass fiber reinforced polyester waste by pyrolysis, solid residue subsequent to pyrolysis was oxidized to recover the glass fibers [48]. These glass fiber webs were subsequently used in the production of composite materials as thermal insulation or as brake blocks. Recycling polypropylene-based composites by means of a dissolution process using an appropriate solvent and filtration to recover the reinforcing agent and the polymer matrix has been reported. Further studies were conducted with the recycled fibers to prepare second-generation composite materials with the same virgin resin, which resulted in better tensile properties but reduced impact performance which was attributed to the influences on the interphase. Similar studies on recyclability of knitted glass thermoplastic liquid molded composite, recycled by a grinding, compounding and injection molding process, have revealed that the recycled cyclic composite demonstrates comparable properties to the baseline material. Thermoforming is a process of reconsolidation of the material into a suitable product shape by application of heat; depending on the fiber type and volume fraction, it is often possible to clean up the material intended for reuse. This method has been recommended for a few products as a viable means of recycling the thermoplastic composite. Non-woven reinforced thermoplastic recycled material is made into a car hatrack by a molding method (thermoforming); the recycled component is shown in Fig. 12.12. This is how, for instance, hatracks or door lining elements are made of recycled materials. In this way production waste that occurs in the manufacturing process could also be recycled to effect a complete cycle of material utilization. Such a conscious approach to recyclability has prompted the composite manufacturing sector to look for the right methods of manufacturing components for composite products to achieve the desired properties, but it still remains that proper legislation in this regard would force the move towards completely recyclable composites.
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12.12 Car hatrack manufactured from recycled thermoplastic composite.
12.9
References
1. B Lauke, U Bunzel and K Schneider, Effect of hybrid yarn structure on delamination behavior of thermoplastic composites, Composites Part A: Applied Sciences and Manufacturing, 1998, 29, 1397–1409. 2. RJ Coldicott and T Longdon, A new family of high performance yarns for composite applications, in Materials and Processing – Move into the 90’s (edited by Benson S, Cook T, Trewin E and Turner RM), Elsevier Science, Amsterdam, 1989, 359–370. 3. L Ye, K Friedrich, J Kastel and YM Mai, Consolidation of unidirectional CF/PEEK composites from commingled yarn prepreg, Composites Science and Technology, 1995, 54(4), 349–358. 4. R Audivert and E Fortuny, Filament feeding in spinning of staple fiber yarns covered with continuous filament, Textile Research Journal, 1980, 50(12), 754. 5. W Oxenham, CA Lawrence, GC East and GT Jou, The physical properties of composite yarns produced by an electrostatic filament-charging method, Journal of the Textile Institute, 1996, 87(1), 78–96. 6. JE O’Connor, Fiber reinforced thermoplastic articles and process for the preparation thereof, US Patent 4800113 (Phillips Petroleum Company, Bartlesville, OK), 24 January 1989. 7. F Pouresfandiari, S Fushimi, A Sakaguchi, H Saito, K Toriumi, T Nishimatsu, Y Shimizu, H Shirai, YI Matsumoto and H Gong, Spinning conditions and characteristics of open-end rotor spun hybrid yarns, Textile Research Journal, 2002, 72(1), 61–70. 8. A Ramasamy, Y Wang and J Muzzy, Braided thermoplastic composites from powdercoated towpregs. Part II: Braiding characteristics of towpregs, Polymer Composites, 1998, 17(3), 505–514. 9. GM Abbott and G Freischmidt, Wrapped-yarn reinforced composites. II. Composite properties, Composites Science and Technology, 1985, 24(2), 147–158. 10. M Acar, AJ Alexander, RK Turton and GR Wray, Analysis of the air-jet texturing process. II. Experimental investigation of the air flow, Journal of the Textile Institute, 1986, 77(1), 28–43. 11. VK Kothari, AK Sengupta and J Srinivasan, Mechanism of the air-jet texturing process: need for reappraisal, in Man-Made Fiber Year Book 1990 (Chemiefasern/ Textilindustrie), 74–77. 12. M Acar and GR Wray, New insights into the mechanism of loop and entanglement formation., in Air Jet Texturing: Present and Future, Loughborough University of Technology, Loughborough, UK, 1987, 9/1–9.
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13. G Bock and J Lunenschloss, Air jet stream and loop formation in aerodynamic texturing, Chemiefasern/Textilindustrie, 1981, 31/83(5), 380–384, PE41. 14. RL Sassa, Composite fiber of commingled fiberglass and polytetrafluoroethylene and method of producing same, US Patent 5456983 (W.L. Gore & Associates, Inc., Newark, DE), 16 September 1994. 15. HJ Oswald, RH Butler and HL Li, Apparatus and method for producing commingled continuous variable texture yarn, US Patent 4467507 (Allied Corporation, Morris Township, Morris County, NJ), 12 March 1982. 16. AC Handermann, Process for preparing thermoplastic matrix fiber reinforce prepregs and composite products structure formed thereof, US Patent 5227236 (BASF Aktiengesellschaft, Ludwigshafen, Germany), 13 July 1993. 17. FR Cramton, Method for commingling and orienting colored sets of thermoplastic filaments, US Patent 3790655 (E.B. & A.C. Whiting Company, Burlington, VT), 5 February 1974. 18. M Sakaguchi, A Nakai, H Hamada and N Takeda, The mechanical properties of unidirectional thermoplastic composites manufactured by a micro-braiding technique, Composites Science and Technology, 2000, 60(5), 717–722. 19. M Acar, RK Turton and GR Wray, Analysis of the air-jet yarn-texturing process, IV – Fluid forces acting on the filaments and the effects of filament cross-sectional area and shape, Journal of the Textile Institute, 1986, 77(4), 247–254. 20. I Kruci n´ ska, E Klata, W Ankudowicz and H Dopierała, Preliminary studies on the manufacturing of hybrid yarns designed for thermoplastic composites, Fibers and Textiles in Eastern Europe, 2000, 8(2), 61–65. 21. N Svensson, R Shishoo and MD Gilchrist, Manufacturing of thermoplastic composites from commingled yarns – a review, Journal of Thermoplastic Composite Materials, 1998, 11, 22–56. 22. TG Gutowski, A resin flow/fiber deformation model for composites, SAMPE Quarterly, 1985, 16(4), 58–64. 23. P Offerman, D Diestel, E Mäder and T Hübner, Development of commingling hybrid yarns for thermoplastic composites, Technische Textilien, 2002, 45(1), E12–E14. 24. BD Choi, O Diestel and P Offerman, Commingled CF/PEEK hybrid yarns for use in textile reinforced high performance rotors, in 12th International Conference on Composite Materials (ICCM), Paris, 5–9 July 1999, 796–806. 25. I Kruci n´ ska, E Klata, W Ankudowicz and H Dopierała, Influence of the structure of hybrid yarns on the mechanical properties of thermoplastic composites, Fibers and Textiles in Eastern Europe, 2001, 9(2), 38–41. 26. S Mazumdar, Composites manufacturing: Materials, Product and Process Engineering, CRC Press, Boca Raton, FL, 2002, Chapter 6. 27. BP Van West, RB Pipes and SG Advani, The consolidation of commingled thermoplastic fabrics, Polymer Composites, 1991, 12(6), 417–427. 28. R Phillips, DA Akyüz and JAE Manson, Prediction of the consolidation of woven fiber reinforced thermoplastic composites. Part I Isothermal case, Composites Part A: Applied Sciences and Manufacturing, 1998, 29A(4), 395–402. 29. S Saiello, J Kenny and L Nicolais, Interface morphology of carbon fiber/PEEK composites, Journal of Materials Science, 1990, 25, 3493–3496. 30. NA Mehl and L Rebenfeld, Computer simulation of crystallization kinetics and morphology in fiber-reinforced thermoplastic composites. I. Two-dimensional case, Journal of Polymer Science. Part B: Polymer Physics, 1993, 31(12), 1677– 1686.
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31. WS Kuo and J Fang, Processing and characterization of 3D woven and braided thermoplastic composites, Composites Science and Technology, 2000, 60(5), 643–656. 32. V Klinkmuller, MK Um, M Steffens, K Friedrich and BS Kim, A new model for impregnation mechanisms in different GF/PP commingled yarns, Applied Composite Materials, 1994, 1, 351–371. 33. A Ramasamy, Y Wang and J Muzzy, Braided thermoplastic composites from powder-coated towpregs. Part III: Consolidation and mechanical properties, Polymer Composites, 1998, 17(3), 515–522. 34. L Li, S Wang and J Yu, Mechanical properties of commingled yarn composites, Indian Journal of Fiber and Textile Research, 2002, 27(3), 287–289. 35. M Stevanovic, M Kostic, T Stecenko and D Briski, Impact behaviour of CFRP composites of different stacking geometry, Composites Evaluation, Proc. TEQ, C87, 78–83. 36. KB Su, Delamination resistance of stitched thermoplastic composite laminates, in Advances in Thermoplastic Composite Materials, (edited by GM Newaz), ASTM STP 1044, 1989, 279–300. 37. MB Dow and DL Smith, Damage tolerant composite materials produced by stitching carbon fabrics, 21st Int. SAMPE Tech. Conf., September 1989. 38. X Diao, L Ye and YW Mai, Fatigue behaviour of CF/PEEK composite laminates made from commingled prepreg. Part I: Experimental studies, Composites Part A: Applied Sciences and Manufacturing, 1997, 28A, 739–747. 39. MD Gilchrist, N Svensson and R Shishoo, Interlaminar fracture of commingled GF/ PET laminates, Journal of Composite Materials, 1998, 32(20), 1808–1835. 40. H Yoon and K Takahashi, Mode I interlaminar fracture toughness of commingled carbon fiber/PEEK composites, Journal of Materials Science, 1993, 28, 1849–1855. 41. N Svensson, R Shishoo and MD Gilchrist, Fabrication and mechanical response of commingled GF/PET composites, Polymer Composites, 1998, 19(4), 360–369. 42. JAM Ferreira, JDM Costa, PNB Reis and MOW Richardson, Analysis of fatigue and damage in glass-fiber-reinforced polypropylene composite materials, Composites Science and Technology, 1999, 59(10), 1461–1467. 43. BD Choi, O Diestel and P Offerman, CF-PEEK commingling hybrid yarns for textile reinforced light weight rotors – Situation and developmental perspectives, Chemical Fibers International, 2002, 52(4), 258. 44. V Mallick, Thermoplastic composite based processing technologies for high performance turbomachinery components, Composites Part A: Applied Sciences and Manufacturing, 2001, 32, 1167–1173. 45. AK Bledzki and J Gassan, Composites reinforced with cellulose based fibers, Progress in Polymer Science, 1999, 24, 221–274. 46. Composites recycling technology wins award, Reinforced Plastics, March 2003, 48(3), 32. 47. NE Zafeiropoulos, PC Varelidis, CD Papaspyrides, T Stern and G Marom, Characterisation of LDPE residual matrix deposited on glass fibers by a dissolution/ reprecipitation recycling process, Composites Part A: Applied Sciences and Manufacturing, 1999, 30, 831–838. 48. MC Adrian and TW Paul, Characterisation of products from the recycling of glass fiber reinforced polyester waste by pyrolysis, Fuel, 2003, 82, 2223–2230.
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Shape memory polymer yarns
T. W a n, Nanjing University of Information Science and Technology, P. R. China
Abstract: Shape memory polymers (SMPs) are smart materials that have the same recoverability and shape memory as NiTi alloys. SMPs have great potential in the clothing and textiles industries due to their similarity to textile structures, as well as uses in the construction of medical devices, micro-electromechanical systems, etc. After introducing their remarkable thermal–mechanical properties, this chapter investigates the key aspects of synthesizing, manufacturing and programming SMP yarns, and goes on to consider how to expand the applications of shape memory polymers to other fields. Future trends in this area are identified. Emphasis is placed on recently developed shape memory nanocomposites and laminated hybrid composites, which have been designed to have enhanced shape memory recovery stress and two-way shape memory. Keywords: shape memory polymer yarn, nanocomposites, shape memory effect, shape recovery, recovery stress.
13.1
Introduction
Shape memory polymers (SMPs) are a novel class of smart materials that can be induced to recover from a temporary deformed state to their original (permanent) shape by an external stimulus or trigger, such as a change in temperature (Lendlein and Kelch, 2002). A considerable number of SMPs with applications in the textile industry have been published or patented. Representative materials that are frequently cited in the literature include polynorbornene, poly(transisoprene), styrene–butadiene copolymers, ethylene–vinyl acetate copolymer, and some polyurethane elastomers (Otsuka and Wayman, 1998, Lendlein and Kelch, 2002; Wei et al. 1998; Nakayama, 1990; Kim et al., 1996). SMPs are intrinsically capable of a shape memory effect, although the mechanisms are dramatically different from those of metal alloys. The unique behaviour of shape memory alloys is based on the temperaturedependent austenite-to-martensite phase transformation on an atomic scale. Thus a temporary shape can be fixed at a single temperature, and recovery occurs upon heating to beyond the martensitic transformation temperature. In contrast, SMPs achieve temporary strain fixing and recovery through a variety of physical means, the underlying large extensibility resulting from the intrinsic elasticity of polymeric networks. 429 © Woodhead Publishing Limited, 2010
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The shape memory effect (SME) of SMPs is characterized by shape recovery and shape fixity, and is unique for polymers with micro-phaseseparated heterogeneous structures. It is due to thermodynamic incompatibility between hard segments (which relate to the maximum thermal transition temperature) and soft segments (which relate to the second highest thermal transition temperature). The domains of a hard segment act as net points, while chain segment domains in a soft reversible segment act as molecular switches. To display shape memory functionality for a particular application, the polymer network has to be temporarily fixed in a deformed state under specific conditions. This requires the deformed chain segments, which are under external stress, to be reversibly prevented from recoiling, and is achieved by introducing reversible net points such as molecular switches. The reversible phase, with the melting or glass transition temperature of the soft segments, holds the temporary deformation. The fixed phase involves the hard segments, which are covalently coupled to the soft segments and inhibit plastic flow through the presence of physical or chemical cross-linkage points between them, thus memorizing the permanent shape (Kim et al., 1996; Li et al., 1997; Lin and Chen, 1998a, 1998b; Takahashi et al., 1996; Lee et al., 2004). The efficiency of a shape memory polymer is empirically controlled by its composition, as defined by the polymer’s chemical structure, molecular weight, the morphology of the phase separation, phase composition, phase distribution, fraction and size of amorphous and crystalline domains (Lendlein and Kelch, 2002; Ohki et al., 2004). SMPs are an important smart material with potential in both academic and industrial settings, having low manufacturing costs, good processing ability, high shape recoverability, and a broader range of shape recovery temperatures than shape memory alloys (SMA) (Lendlein and Kelch, 2002; Wei et al., 1998; Hayashi et al., 1995). Compared with shape memory alloys, SMPs are likely to be more suited to textiles and clothing, as well as related products in actuators, sensors and biomaterials. One reason for this is that the mechanical properties of SMAs can only be adjusted within a limited range (maximum deformation of about 8%), whereas SMPs are inherently recoverable even with a deformation of several hundred percent. However, although intensive research on SMPs has been conducted in both academia and industry in the past 20 years or so, the understanding of how to prepare SMP fibres is still in its infancy (Meng and Hu, 2008a). Compared with SMP bulks, SMP fibres have certain highly desirable mechanical properties as a result of the inherent molecular orientation of fibres (Meng and Hu, 2008a). Such properties contribute to the versatility of SMPs, allowing them to be used in applications ranging from the manufacture of biomedical materials to high performance sensors. In particular, their high recoverability broadens their applicability further in textile production – for the manufacture of woven fabrics such as fabrics, swimwear, sportswear,
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ladies’ hosiery, corsetry and medical hosiery, where they are capable of responding dynamically to fluctuations in heat and moisture levels, thus ensuring improved comfort for the wearer. SMP fibres can be spun alone, or blended with other fibres.
13.2
Thermo-mechanical behaviour of shape memory polymers (SMPs)
A large volume of literature regarding the general thermo-mechanical behaviour of SMPs exists (Tobushi et al., 1998; Lendlein and Kelch, 2002). Materials with the unique ability of being able to recover their original, permanent shape from a fixed temporary shape only when triggered by some specific external stimulus, are classified as demonstrating a shape memory effect (SME). In particular, SMPs are able to change shape in response to variations in temperature. For SMPs of the polyurethane series, the glass transition temperature (Tg) may be set to approximate room temperature, and their defining characteristics of shape recovery, shape fixation, etc., may be quite distinct at temperatures above and below this critical Tg value. In Fig. 13.1, an SMP material based on a post-polymerized AB-polymer network is shown as an example of thermally induced SME. In SMP materials, the unconstrained recoverable material strain limits are of the order of 100%, whereas in shape memory metals or ceramics, this value is about 10% and 1% strain, respectively. A typical schematic of the thermo-mechanical behaviour of SMP is illustrated in Fig. 13.2. Thermo-mechanical processes, such as hot compression, extrusion or injection moulding, can be used to process thermoplastic SMPs to give them a memorized permanent shape. At temperatures higher than the transition temperature Tg, in the first step of the cycle, SMPs are mechanically deformed into the desired temporary shape. The temporary shape is then fixed by some constraint while lowering the temperature in the second step. As the temperature decreases, the stress needed to maintain the shape gradually diminishes. After the SMP chain segments have been frozen in a temporary position by thermally reversible interactions between the molecular chains, the constraint is then removed and the induced shape is fully retained in the third step. Here, the strain fixity rate is defined as the difference in the shapes found after stages 1 and 3, and it can be a criterion for assessing shape memory performance because large strain fixity rates imply enhanced micro-phase separation in SMPs. The rigidity of polymer chains in the soft segment is found to decrease upon heating in stage 4, and the frozen stress balance breaks so that the SMP returns to its original, permanent shape. This cycle is then repeated (Lin and Chen, 1998a, 1998b; Otsuka and Wayman, 1998; Lendlein and Kelch, 2002; Lendlein et al., 2001). Since the hard segments act like net points and remain rigid throughout
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t=0s
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t = 15 s
t = 18 s
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13.1 Series of photographs showing the macroscopic shape memory effect of an AB-polymer network. The pictures show the transition from temporary to permanent shape at 70°C within 20 s.
the memorizing process (stage 2 of Fig. 13.2), it is the variation of rigidity in the soft segment with temperature that determines both the deformation to the temporary shape and the recovery to the permanent shape. Depending on the molecular arrangement of the soft segments, the transition in rigidity of polymer molecules is governed by the glass transition temperature (Tg); and accordingly, as illustrated in Fig. 13.3, a drastic change in elastic modulus is observed in the vicinity of Tg. Above Tg, these materials are soft, whilst below Tg their hardness increases rapidly until they become rigid and eventually brittle. Thus, SMPs with different mechanical properties can be developed by controlling Tg of the soft segment, the level of micro-phase separation, and the structure of the hard segment, leading to a variety of potential applications (Shim et al., 2006; Gall et al., 2002; Beloshenko et al., 2003; Hosoda et al., 2004; Hampikian et al., 2006).
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Stress Fixed shape
sl sm 3 2
Tl
eu
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Ttrans Permanent shape
sm 1 Th
ep
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Temperature
13.2 Typical thermo-mechanical behaviour of SMP. (Seok et al., 2007). 1010
Glassy region
Tg region
Rubbery region
E (Pa)
109 108 107 106
Tg Temperature
13.3 Variations of SMP elastic modulus with temperature (Sokolowski et al., 2007).
The shape memory effect in SMPs is distinct from that in SMAs. At temperatures above its Tg, an SMP will only return to its original shape provided there are no external forces applied. Unlike SMAs, externally triggered shape reversal in SMPs can be described as metamorphic, in that the polymer exhibits a gradual change in shape during transformation. The SME is trained through a series of cyclic thermo-mechanical processes. An example training process in yarns of specimen SMPs is as follows:
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1. Specimens are stretched at a high temperature, Thigh = Ttrans + 20°C, to an elongation of 100% strain. 2. Deformed specimens are cooled down to a low temperature Tlow (room temperature), whereupon the deformations are fixed. 3. At Tlow the external force on the specimens is removed. 4. The deformation is recovered by heating the samples back up to Thigh. 5. The cycle reverts to step 1 and repeats. The shape memory effect in SMPs is described by the shape memory properties of shape fixity (SF), shape recovery ratio (RR) and recovery stress. The relationship between stress and strain is recorded in the cycles. As illustrated in Fig. 13.2, let em, eu and ep, respectively denote the maximum strain in the cyclic tensile tests, the residual strain after unloading at Tm–20 °C, and the residual strain after shape recovery; the shape fixity (Rf) and the shape recovery ratios (Rr) can be calculated using:
Rf = eu/em × 100%
[13.1]
Rr = (em − ep)/em × 100%
[13.2]
The unique characteristics and properties of SMPs make these materials highly attractive for applications in many commercial settings. Their advantages over SMAs are summarized below: ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑
lightweight, typical density about 1.13–1.25 g/cm3 compared to 6.4–6.5 g/cm3 for NiTi Wide range of allowable glass transition temperatures, Tg = –70°C to +70°C, allowing for applications in a variety of thermal environments Shape recovery of up to 400% of plastic strain, compared to 7–8% for SMA Reversible changes in elastic modulus between the glassy and rubbery states of the polymers (can be up to 500 times the original value) Excellent biocompatibility allowing for biomedical applications Reversible changes characteristically from moisture-permeable to waterproof during transition from rubbery to glass state Ease of processing, including moulding, extrusion and conventional machining low cost, –10% of existing shape memory alloys (SMA) characterized by low recovery forces, i.e. low actuating forces, and cannot be utilized in high power actuators.
13.3
Manufacture of shape memory polymer (SMP)-based yarns
Before being used in mass-production yarns, SMPs were synthesized for specific applications. For example, thermoplastic shape memory polyurethanes with © Woodhead Publishing Limited, 2010
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various hard segments were synthesized with a pre-polymerization method using poly-diols, di-isocyanate and a chain extender. The SME of shape memory polyurethane fibre is characterized by its micro-phase-separated heterogeneous structure, which is composed of a hard segment phase and a soft segment phase. The design required will dictate the choice of SMP yarn formation (e.g. extruder or injection moulding) and state (solution or molten). A few key processes for manufacturing SMP-based yarns are introduced below.
13.3.1 Melt spinning A raw resin pellet was dried in a vacuum for 8 h in a hopper circulation oven at 80°C until moisture levels decreased to 0.03%. If the resin is not dried, the polymer’s viscosity becomes too low when melted, causing deformation by foaming, flashing and dropping at the nozzle. Shape memory polyurethane filaments were spun using a 20 mm single extruder with high-purity nitrogen protection. The winding-up speed was from 10 m min−1 to 50 m min−1, with an overfeed speed of 10 m min−1. The laminar air temperature was 22°C. The extruder head pressure was 5.00 MPa and the spin pack pressure was 22.00 MPa (Meng and Hu, 2008a, 2008b; Stylios and Wan, 2007). The temperature profile for processing an SMP filament of 0.4–0.6 mm diameter using an extruder of diameter 1 mm is as follows: ∑ Rear (feed zone) T: 170–180°C ∑ Centre (compression) T: 175–185°C ∑ Front (metering zone) T: 170–180°C. The key to this operation is to control the viscosity of the SMP in the nozzle of the extruder, while maintaining uniform melting of the polymer. The viscosity of SMPs is more temperature-dependent than that of traditional polymers, requiring stricter temperature regulation and processing controls. In order to control the diameter of the SMP filament, the extrusion rate also has to be regulated.
13.3.2 Wet spinning Details of the wet spinning process are described in Ji et al. (2006) and Zhu et al. (2006). The concentration of solids in the final polyurethane solution (PU solution) in DMF (N,N-dimethylformamide) was adjusted in the range of 20–30 wt% to satisfy the associated viscosity requirements under which the PU solution is spun into fibres on the equipment after filtration and degassing at 100°C, as shown in Fig. 13.4. With the equipment shown in Fig. 13.4(a), an SMP solution was extruded from a spinneret with 30 pinholes each 0.08 mm in diameter into a coagulation bath at a speed of 6
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smpu solution
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Drying
Spinneret Winding Coagulation bath To recovery (a)
Drawing roll 1
Drawing roll 2
Hot oven Taking up winder
Initiate fibre (b)
13.4 Schematic diagrams of (a) the wet spinning equipment, and (b) heat setting of shape memory fibres (Ji et al., 2006, Zhu et al., 2006).
m min–1 under pressure exerted by the compressed nitrogen. The coagulated fibres were then extracted onto a group of rolls at 10 m min–1 and passed through a water bath where they were rinsed. Next, the rinsed fibres were passed through a hot chamber to undergo drying. The dried fibres were subsequently wound up by a winder. To eliminate the internal stress stored in the spinning process, a heat treatment was carried out, during which the fibres were passed through a heated oven (see Fig. 13.4(b)) of length 2 m, maintained at a temperature of 120°C.
13.3.3 Transfer of SME to a generic fibre after the finishing process The subtle interaction between SMPs and cellulose fibres within fabrics remains a critical issue for understanding their thermal–mechanical properties, and thus their shape memory behaviour in cotton fibres. Various finishing processes for transferring the SME to cotton or generic polymer yarn
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have been proposed (Li et al., 2004; Liem et al., 2007). A highly viscous resin adhesive was prepared by dissolving polyurethane in toluene or N,Ndimethylformamide. The shape memory polyurethane powder and the resin adhesive were mixed in a certain ratio. The cotton or polymer yarn was then immersed in the SMP solution or the mixture, passed through rolls by means of the rollers, and subjected to a pad–dry–cure process. After padding twice between two rubber rollers at a pressure of 3 MPa, the fabrics were chemically treated with finishing agents. The wet fabric was then transferred to an oven, dried at 50°C in a vacuum chamber for 6 h to degas in order to remove the solvent, and then cured at 120°C for 3 min.
13.4
Applications
13.4.1 Breathability, clothing comfort, wrinkle recovery, etc. Shape memory woven cotton fabrics/garments and shape memory fibres have been under development ever since smart textiles and clothing applications for SMPs were described by Hu et al. in 1998 (Hu et al., 2004; Hu, 2006). Shape memory fabrics treated with SMP have excellent hand, shape retention, dimensional stability, durability, wrinkle resistance, flat appearance, bagging recovery, comfort for the wearer, and ease of care, even under water and at high temperatures. But although SMPs already have applications in the textile industry, their technological potential has not been fully exploited. All comfortable clothing demonstrates interactions with the human body, such as variable breathability in response to varying temperature. When the temperature of the skin differs by more than 3.0°C from the ideal body temperature, the wearer will begin to feel uncomfortable (Tao, 2001; Mattila, 2006). In a temperature-regulating clothing system, phase change materials (PCMs) are used to regulate temperature fluctuations. The phase transition temperature should be in the range of 10–50°C (Bryant, 1999; Colvin, 1999). When the temperature is higher, PCMs absorb and store heat energy with no temperature increase; when the material cools down, the latent heat is released to the human body. An SMP fibre, a temperature-regulating fibre with a large latent heat-storage capacity of about 100 J/g, was fabricated by melt spinning (Meng and Hu, 2008b). The PEG soft segment phase transfer of the SMP between crystalline and amorphous states results in heat storage and release. At temperatures above the PEG phase melting transition, the SMPs remain solid because the hydrogen-bonded hard segments restrict the free movement of soft segments. Since air has very low conductivity, heat insulation in newly developed materials is achieved by trapping as much air as possible in the microspaces between and within fibres, thus minimizing heat losses by convection. A
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further contribution to the insulating effect arises from the air entrapped between the fabric and the skin. This is akin to the principle of keeping warm by wearing multilayered clothing in cold weather in order to trap more air. Wind speed and wind chill factors associated with low temperatures must also be considered in the design of clothing, because the movement of air disturbs the boundary air layer of the clothing, thus changing its insulation capability (Walker, 1983). The prototype design has a layer of shape memory yarn incorporated between adjacent layers of clothing. The films can be made on an extrusion/calendering line and the laminates can be compression-moulded using conventional equipment. To promote the circulation of air and moisture vapour within the interstitial space, as well as to reduce the weight of the film, holes and cutouts can be made in the laminate. When the temperature of the outer layer of clothing has dropped sufficiently, the shape memory layer should shrink linearly by about 3% and become rigid, while the conventional elastomer remains largely unaltered, thus the polyurethane film broadens the air gaps between layers of clothing. As a result, an out-of-plane deformation of the laminate is expected, and non-evaporative heat loss can be controlled. Of course, the deformation should be reversible if the outer layers of clothing become warmer again. One factor that determines garment quality is the ability to recover from wrinkling, i.e. to retain a smooth appearance and to avoid crease retention after repeated home laundering (Xu and Cuminato, 1998). Fabric and garment manufacturers have made considerable efforts to improve anti-wrinkling properties by overcoming the ruggedness of fabric surfaces (Cheng and Kai, 1998). According to the shape memory principles described above, external stimuli such as cooling and heating may affect the shape of materials, and this is used to improve smoothness, crease retention and wrinkle recovery by incorporating a thermally induced SME into woven wool garments. Woven wool fabrics treated by this method show enhanced smoothness, crease retention and wrinkle recovery after washing and tumble drying. In fact, garment wrinkling can even be recovered completely and quickly using a travel hairdryer to provide hot air.
13.4.2 Engineering fabric aesthetics With a surge of designers, technologists and engineers keen for mutual cooperation, textile design and manufacture have developed beyond the use of traditional materials, techniques and methodologies, allowing the incorporation of specialized skills and unconventional materials. Research has been conducted into textiles with shape memory attributes conferred by using engineering SMPs incorporated into a woven structure (Stylios and Wan, 2007; Chan et al., 2002). These textiles can change shape and interact with
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the surroundings, in contrast to the biomedical and engineering applications that the SMPs were principally developed for, such as constructing ligaments and vascular stents and in robotics. Figures 13.5 and 13.6 illustrate the shape memory performance of various composite textiles densely and uniformly woven with SMP yarn of 0.4 mm diameter. Conventional nylon yarns or polymer yarns of assorted fine wire
(a)
(b)
(c)
13.5 Shape memory recovery of SMP composite loosely woven fabric with SMP yarn at 50°C with recovery time (a) 0 s, (b) 30 s and (c) 60 s.
(a)
(b)
13.6 Shape memory recovery of SMP composite loosely woven fabric at 50°C with recovery time (a) 0 s and (b) 30 s.
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with differing performance were blended and woven with SMP yarn in these samples. The SMP yarn was woven spaciously and loosely across the fabric weft to allow room for the SME to take place. The initial planar shape of the SMP composites was fixed by exerting an external stretch force when the sample was placed into a frozen state. The SME then deformed the fabric from its original, flattened shape at low temperature to a rough and embossed matrix with convex edges upon contraction at high temperature. In this case, complete contraction occurred because of the dramatic decrease in the elastic modulus of the SMP yarn when the environmental temperature rose above Tg. These shrunken fabrics exhibit rough and embossed edges, the convex edges appearing predominantly in regions consisting only of SMP yarns. The recovery process is metamorphic, so the polymer experiences a gradual shape variation during transformation. When blended with various kinds of flexible and light yarns, fabric designs based on SMP yarns can display interesting aesthetic appeal, as shown in Figs 13.7 and 13.8, depending on the fabric design and SMP-specific training. However, since the SME in existing SMP yarns is only one way, it is difficult to perform an invert shape variation for these composite textiles. This is solved by adding a reinforcement material with a high elastic modulus to the SMP matrix. There is interest in more complex shape variations, such as polymer fabric reinforcements with high elastic modulus crosslinking with SMP yarn in a fabric structure, as demonstrated in elastic memory materials used in spacecraft (Meink et al., 2001).
13.4.3 Applications in the medical field Since El Feninat et al. (2002) and Lendlein and Kelch (2005) reported a PCL-based biodegradable polymer and demonstrated its potential in medical applications, biodegradable SMPs have been the focus of considerable research. Different clinical devices contact or are inserted into the human body. The combination of shape memory capability and biodegradability possessed by certain SMPs is especially advantageous for medical devices requiring shape restoration and/or self-deployment, where the emphasis is on minimally invasive surgery (Ratna and Karger-Kocsis, 2008). The polymers provide a convenient means of inserting bulky implants in a compacted state (a temporary shape). They are inserted into the human body in string form through a small incision. When influenced by body heat, they expand back into their original, permanent shape, as shown schematically in Fig. 13.9. The biodegradability of the implant ensures that it will dissolve completely in the body over time, for instance a stent in a blocked artery. Biodegradable SMPs are especially useful in situations where a medical structure incorporated into the body is not intended to be permanent. While scaffolding devices
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(a)
(b)
(c)
13.7 Shape memory recovery of SMP composite loosely woven fabric with flexible yarn at 50°C with recovery time (a) 0 s, (b) 30 s and (c) 60 s.
for assisting in bone and tissue repair might call for biodegradable SMPs, the option of permanent prosthetic implants is also possible. The use of biodegradable SMPs as an intelligent suture for wound closure provides an interesting example (Sokolowski et al., 2007). SMPs used in surgical sutures could allow optimized tightening of the knot. The suture could be applied loosely in its temporary shape, and when the temperature is raised to above Tg, the knot would shrink and tighten, applying optimum force, as shown in Fig. 13.10. This technique is effective for minimizing scar formation and reduces the risk of foreign infection. These intelligent polymers also have potential for probing neurons in the
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13.8 Shape memory recovery of SMP composite woven fabric samples with varied fabric design at 50°C with recovery time 30 s.
Temporary shape
Permanent shape
13.9 Representation of recovery of a string-like material to a tubular device (Ratner and Karger-Kocsis, 2008).
20°C
37°C
41°C
13.10 The medical possibilities of a shape memory polymer (SMP) were recently demonstrated in the form of a self-tightening knot (Sokolowshi et al., 2007).
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brain or engineering a tougher spinal bone. Another application of SMPs is targeted drug delivery, where SMP matrices release drugs by a change in structure. Often a hydrolysis reaction will occur, resulting in cleavage of bonds and release of the drug as the matrix breaks down into its constituent, biodegradable components.
13.4.4 Some further applications The scope of these smart polymers can be extended to the automotive, electronics and aviation industries, all of which are likely to reap innovative benefits from their intrinsic shape-changing properties. In the automotive industry, SMPs can feasibly be used in vehicle bumpers, fascia panels, or other parts of the exterior car body sheath which are vulnerable to crashes and deformations and consequently the formation of dents. Any indentation/ damage due to involvement in a crash or accident suffered by a car sheath manufactured from SMPs will result in a temporary form. Upon reheating, the SMP components would change back to the undamaged original form, allowing for rapid and effective repair. SMP yarns are expected to play a major role in the development of morphing wing technology in the aviation industry, where the ambition is to produce planes which can respond to dynamic changes in flight conditions by adjusting their shape continuously so as to maximize efficiency at all times. Wings can be constantly adjusted to compensate for gusts or patches of lift, so the aircraft of the future will be in a constant state of flux, altering wing shape and control surfaces, and narrowing or flaring its engine exhausts. The incorporation of structural or functional polymers in micro-electromechanical systems (MEMS) raises new issues and challenges. Recent work has concluded that certain MEMS sensor applications will benefit greatly from the use of SMPs (Gall et al., 2004). Liu (2007) provides a comprehensive review of the recent state of polymer-based MEMS, including materials, fabrication processes, and representative devices such as microfluidic valves and tactile sensors. The fundamental challenges include the dispersion of nanoscale reinforcements in polymer matrix materials, the fabrication of micron-scale MEMS from nanocomposites by micro-casting and photopolymerization, and the realization and characterization of functional shape memory properties at micron scales. If successful, research on SMP-based nanocomposites in MEMS will impact upon microscale actuation in complicated environments for many biomedical and microsensor applications. The potential applications of such devices include microvalves, micropumps, microgrippers, microswitches, etc. The expansion of human and robotic exploration dictates the need for novel and complex modes of communication. Visually, these would include layered architecture that supports hyperspectral imaging, synthetic aperture
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radar, high-definition television, and telemedicine. For antennas as large as those needed, critical performance specifications include low aerial density, high packaging efficiency, accurate surface geometry to ensure high reflector efficiency, and reliable deployment. Johns Hopkins University and the NASA Glenn Research Center are currently developing inflatable membranes with a rigid torus, and a hybrid shape memory composite that incorporates a fixed central reflector that serves as a backup antenna in case of deployment problems with the main aperture (Lin et al., 2006). The objective is to develop large gossamer antennas for use in deep space, e.g. missions to the Moon, or Mars, which require them to be cost-effective, have very low mass, and have improved deployment reliability, all while maintaining accurate dimension tolerances.
13.5
Future trends
We have already seen that SMPs are characterized by their remarkable recoverability and SME. However, most SMPs exhibit a one-way shape memory, and lack two-way memory capability (Lendlein and Kelch, 2002). SMPs also have relatively low recovery stress, usually 1–3 MPa compared to 0.5–1 GPa for shape memory metal alloys (Lendlein and Kelch, 2002). This has become the main limiting factor in many applications, especially in cases where SMPs need to overcome a large resisting stress during shape recovery.
13.5.1 SMP nanocomposite combined with nano reinforcement phase In order to significantly increase the shape recovery stress of SMPs destined for structural applications, some reinforcements, such as organoclay, carbon nanofibre (CNF), silicon carbide (SiC) and carbon black (CB), have recently been selected as fillers to enhance the stiffness of SMPs (Gall et al., 2000, 2002; Bhattacharya and Tummala, 2002). Figure 13.11 illustrates the shape recovery stresses of SMP multi-walled carbon nanotube (MWNT) fibres with different MWNT contents. When compared with those of pure SMP fibres, the recovery stresses of SMP-MWNT fibres with 1.0–3.0 wt% MWNT content are much higher due to better interface properties, and can also attain maximum values much more quickly. It has also been noted that properly incrementing the weight fraction of reinforcements significantly improves storage elastic modulus, and the CNT/SMP nanocomposites showed a good SME in modulus strength (Ash et al., 2001; Bhattacharya and Tummala, 2002; Gall et al., 2002). While the recovery stress of pure SMP fibre is primarily attributed to characteristics of the hard segment phase, for SMP fibres with a
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4 Time (min)
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13.11 Shape recovery stress of SMP fibres with different MWNT (multi-walled carbon nanotubes) contents (Gall et al., 2000).
reinforcement phase it may also be ascribed to strong interactions between the reinforcement phases and the hard segment. Composite stiffness and recoverable strain levels were found to depend strongly on the volume fraction of the discontinuous reinforcement. However, when the MWNT content is continuously increased to 5.0 wt%, the shape recovery stress begins to fall. This may be due to the inhomogeneous distribution of MWNT and the deteriorating surface quality of reinforcement composites, which can disturb the fundamental polymer networks responsible for shape memory functions. Additionally, it has been observed that incorporation of particles also changes the crystallization behaviour and activation energies of relaxation processes in polymers. The addition of other particles to SMPs, such as carbon nanotubes, carbon particles, conductive fibres and nickel zinc ferrite ferromagnetic particles, alters not only their stiffness and recoverable strain levels but also their electrical and magnetic properties. In this case, shape recovery can be triggered by various external stimuli, not only heat (Hu et al., 2005; Liu et al., 2007; Lendlein et al., 2005) but also light (Jiang et al., 2006; Lendlein et al., 2005), joule heating in an electric field (Leng et al., 2007; Koerner et al., 2004; Paik et al., 2006; Schmidt, 2006), induction heating in a magnetic field (Buckley, 2006), etc. Although a lot of research focusing on stimuli-responsive SMPs and their composites has been conducted in this area to date, few conclusive, mutually corroborating results have been obtained.
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13.5.2 SMP hybrid combined with non-SMP As described above, permanent shape memory in the SMPs themselves relies on the hard segment phase crosslinking within the structure, while the soft segment phase helps set the frozen temporary shape below Tg. Thus, after shape memory training, SMPs acquire the ability to remember the permanent shape above Tg, but not the temporary frozen shape below Tg. By hybridizing shape memory materials with other functional or structural materials, smart composites can be fabricated which integrate a multitude of specialized functions or properties of the separate, constituent materials to achieve complex responses to environmental changes. Tremendous potential for creating new paradigms for material structural interaction lies in these unique material systems. In polymer laminates consisting of one-way shape memory SMP film from PHAG5000-based shape memory polyurethane and elastic polymer film from PBAG600-based polyurethane, not only can a two-way shape memory effect be achieved, but the reversible deformation is also controllable (Chen et al., 2008). The PHAG5000-based shape memory polyurethane has a crystalline soft segment phase and amorphous hard segment, and shows a good one-way shape memory effect, while the PBAG600-based polyurethane shows an amorphous soft segment phase. As the temperature increases (decreases), the modulus of elasticity of the material decreases (increases). However, as shown in Fig. 13.12, the distinction is that the PBAG600-based polyurethane recovers its modulus gradually as the temperature decreases, while around Tg the PHAG5000-based shape memory polyurethane shows an obvious hysteresis effect in its modulus recovery, which is due to the presence of a soft segment phase. This difference results in the loss of balance in rigidity or stiffness upon cooling. The modulus of a substrate layer is usually much higher than that of an active layer of SMP. As shown in Fig. 13.12, upon heating, the elastic modulus of both layers decreased with the temperature; whereas upon cooling, the modulus of the substrate layer began to increase significantly at 60°C, while the modulus of the active layer increased little until the temperature cooled down to below 25°C. Moreover, the modulus of the substrate layer was usually much higher than that of the active layer. The bending force of the material increases with modulus of elasticity, while the elastic strain is determined by the deformation angle (Ping et al., 2005). Therefore, the resulting bending force of the substrate layer can be complementary to the recovery force of the active layer in the SMP laminate during the recovery process, and in particular during the cooling process. On the basis of this principle, upon heating, the whole SMP laminate bends toward the active layer due to the recovery force of SMP, and a temporary shape (high temperature shape) is preserved when the recovery force is equal to the bending force of the substrate layer. Upon cooling, the bending substrate layer acts as a bias
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0 Temperature (°C)
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13.12 Bending modulus vs temperature (Chen et al., 2008).
spring and leads to a reverse shape change. Then the whole SMP laminate recovers to another temporary shape (lower temperature shape). Similarly, a bi-component fibre designed with a crescent cross-section can produce the desired ‘two-way’ shape memory effect, and can thus be used for manufacturing comfortable apparel (Fred et al., 2005). With reference to Fig. 13.13, the inner (B) and outer (A) components of the fibre crosssection comprise polymer components with the higher (B) and lower (A) thermal expansion coefficients. By selecting and coupling two polymers with significantly different thermal expansion coefficients, a fibre system that is highly sensitive to temperature change will be formed. When the temperature is increased, the cross-section opens up as the inner component experiences a greater expansion than the outer component, and then closes when the temperature is decreased again. Competing thermally induced expansions induce net thermal and elasticity effects in the fibre, allowing the system to remember all temperature-dependent permanent shapes. This system will form a channel cross-section at higher temperatures and resemble a closed hollow fibre at lower temperatures. Compared with ordinary fabric systems, garments constructed from these bi-component fibres will have superior comfort properties in all weather conditions.
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13.13 Fibre cross-section: A and B are two polymers (outer and inner components) in a hollow bi-component fibre (Fred et al., 2005).
13.6
Conclusion
The various desirable attributes and properties that are often unique to SMPs, such as biocompatibility, dependence on temperature fluctuations, and ability to exhibit the shape memory effect, give them potential applications in fields as diverse and disparate as the textile industry, the manufacturing industry, engineering and biomedical science. SMPs have numerous fundamental advantages over SMAs, and the key manufacturing processes for SMP-based yarns, such as melt spinning and wet spinning, can be used to achieve particular desired results. The immediate hope for the future lies in the development of novel shape memory nanocomposites and laminated hybrid SMP composites, in which dissimilar and often unconventional components are bound together to realize new and imaginative effects, ultimately enhancing shape memory recovery stress and two-way shape memory properties. As the use of SMPs in surgical sutures and biodegradable medical equipment suggests, in SMPs we have an example of how, when inspired by perseverance and scientific ingenuity, the discovery of a new product with unexplored properties can lead to the birth, development and eventual diversification of a new field of science. The future is promising.
13.7
References
Ash B J, Stone J, Rogers D F and Schadler L S (2001), ‘Investigation into the thermal mechanical behavior of PMMA/alumina nanocomposites’, Materials Research Society Proceedings, 661, KK2.10.1–6. Beloshenko V A, Beigelzimer Y E, Borzenko A P and Varyukhin V N (2003), ‘Shapememory effect in polymer composites with a compactible filler’, Mech. Compos. Mater., 39(3), 255.
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Bhattacharya S K and Tummala R R (2002), ‘Epoxy nanocomposite capacitors for application as MCM-L compatible integral passives’, Journal of Electronic Packaging, 124(1), 1–6. Bryant Y G (1999), ‘Melt spun fibers containing microencapsulated phase change material’, in: Advances in Heat and Mass Transfer in Biotechnology, ASME International Mechanical Engineering Congress and Exposition, Nashville, TN. Buckley P R (2006), ‘Inductively heated shape memory polymer for the magnetic actuation of medical devices’, IEEE Trans. Biomed. Eng., 53(10), 2075–2083. Chan Y F F, Winchester R C C et al. (2002), ‘The concept of aesthetic intelligence of textile fabrics and their application for interior and apparel’, IFFTI International Conference proceedings, Hong Kong. Chen S J, Hu J, Zhuo H and Zhu Y (2008), ‘Two-way shape memory effect in polymer laminates’, Materials Letters, 62, 4088–4090. Cheng H and Kai S (1998), ‘Easy-care finishing of silk fabrics with a novel multifunctional epoxide’, J. Soc. Dyers Colourists, 114(12), 359–369. Colvin D P (1999), ‘Enhanced thermal management using encapsulated phase change materials: an overview’, in: Advances in Heat and Mass Transfer in Biotechnology, ASME International Mechanical Engineering Congress and Exposition, Nashville, TN. El Feninat F, Laroche G and Fiset M (2002), ‘shape memory materials for biomedical application’, Adv. Eng. Mater., 4, 91. Fred L C, Jacob K I, Polk M and Pourdeyhimi B (2005), ‘Shape memory polymer fibers for comfort wear’, National Textile Center Annual Report: November 2005, http:// www.ntcresearch.org/pdf-rpts/AnRp05/M05-GT14-A5.pdf Gall K, Mikulas M and Munshi N A (2000), ‘Carbon fiber reinforced shape memory polymer composites’, Journal of Intelligent Material Systems and Structures, 11, 877–886. Gall K, Dunn M L, Liu Y, Finch D, Lake M and Munshi N A (2002), ‘Shape memory polymer nanocomposites’, Acta Materialia, 50, 5115–5126. Gall K, Kreiner P, Turner D and Hulse M (2004), ‘Shape-memory polymers for microelectromechanical systems’, Journal of Microelectromechanical Systems, 13(3), 472–483. Hampikian J M, Heaton B C, Tong F C, Zhang Z and Wong C P (2006), ‘Mechanical and radiographic properties of a shape memory polymer composite for intracranial aneurysm coils’, Mater. Sci. Eng. C: Biomimetic Supramol. Syst., 26(8), 1373. Hayashi S, Kondo S, Kapadia P and Ushioda E (1995), ‘Room-temperature-functional shape-memory polymers’, Plast. Eng., 51, 29–31. Hosoda H, Takeuchi S, Inamura T and Wakashima K (2004), ‘Material design and shape memory properties of smart composites composed of polymer and ferromagnetic shape memory alloy’, Science and Technology of Advanced Materials, 5, 503−509. Hu J L (2006), Shape Memory Material for Textiles, China Textile and Apparel Press, June, pp. 375–403. Hu J L, Li Y K, Chung S P and Chan L K (2004), ‘Subjective evaluation of shape memory fabrics’, Proc. Int. Conf. on ‘High Performance Textiles and Apparels’, HPTEX 2004, Kumaraguru College of Technology, Coimbatore, India, Vol. 6, pp. 597–604. Hu L, Ji F L and Wong Y W (2005), ‘Dependency of the shape memory properties of a polyurethane upon thermomechanical cyclic conditions’, Polym. Int., 54(3), 600–605. Ji F L, Zhu Y, Hu J, Liu Y, Yeung L-Y and Ye G (2006), ‘Smart polymer fibers with shape memory effect’, Smart Mater. Struct., 15, pp. 1547–1554. © Woodhead Publishing Limited, 2010
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Jiang H Y, Kelch S and Lendlein A (2006), ‘Polymers move in response to light’, Adv. Mater., 18(11), 1471–1475. Kim B K, Lee S Y and Xu M (1996), ‘Polyurethane having shape memory effects’, Polymer, 37, 5781–5793. Koerner H, Price G, Pearce N, Alexander M and Vaia R A (2004), ‘Remotely actuated polymer nanocomposites – stress-recovery of carbon-nanotube-filled thermoplastic elastomers’, Nature Materials, 3(2), 115–120. Lee S H, Kim J W and Kim B K (2004), ‘Shape memory polyurethanes having crosslinks in soft and hard segments’, Smart Mater. Struct., 13, 1345–1350. Lendlein A and Kelch S (2002), ‘Shape memory polymers’, Angew. Chem., Int. Ed. Engl., 41, 2034–2057. Lendlein A and Kelch S (2005), ‘Degradable, multifunctional polymeric biomaterials with shape-memory’, in: Functionally Graded Materials VIII, Van der Biest O, et al., (eds), Tech Trans Publications, Zurich, Switzerland, pp. 492–493, 219. Lendlein A, Schmidt A M and Langer R (2001), ‘AB-polymer networks based on oligo(ecaprolactone) segments showing shape-memory properties’, Proc. Natl Acad. Sci. USA, 98(3), 842–847. Lendlein A, Jiang H Y, Junger O and Langer R (2005), ‘Light-induced shape-memory polymers’, Nature, 434 (7035), 879–882. Leng J S, Lv H B, Liu Y J and Du S Y (2007), ‘Electroactivate shape-memory polymer filled with nanocarbon particles and short carbon fibers’, Appl. Phys. Lett., 91, 144. Li F K, Zhang X and Hou J N (1997), ‘Studies on thermally stimulated shape memory effect of segmented polyurethanes’, J. Appl. Polym. Sci., 64, 1511–1516. Li Y, Zhang G-C and Xing J-w (2004), ‘Study of wet-sensitive shape memory knitting fabric’, Journal of Functional Polymers, 17(3), 401–405. Liem H, Yeung L Y and Hu J L (2007), ‘A prerequisite for the effective transfer of the shape-memory effect to cotton fibers’, Smart Mater. Struct., 16, 748–753. Lin J K H, Knoll C F and Willey C E (2006), ‘Inflatable membrane reflector and shapememory polymer antenna developed for space and ground communications applications’, 47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 1–4 May 2006, Newport, RI. Lin J R and Chen L W (1998a), ‘Study on shape-memory behavior of polyether-based polyurethanes. I. Influence of the hard-segment content’, J. Appl. Polym. Sci., 69, 1563–1574. Lin J R and Chen L W (1998b), ‘Study on shape-memory behavior of polyether-based polyurethanes. II. Influence of soft-segment molecular weight’, J. Appl. Polym. Sci., 69, 1575–1586. Liu C (2007), ‘Recent developments in polymer MEMS’, Advanced Materials, 19(22), 3783–3790. Liu C, Qin H and Mather P T (2007), ‘Review of progress in shape-memory polymers’, J. Mater. Chem., 17(16), 1543–1558. Mattila H R (ed.) (2006), Intelligent Textiles and Clothing, Woodhead Publishing, Cambridge, UK, p. 981. Meink T, Qassim K and Murphey T (2001), ‘Elastic memory composite materials: Their performance and possible structure applications’, 13th International Conference on composite materials, Beijing, 25–29 June. Meng Q and Hu J (2008a), ‘Self-organizing alignment of carbon nanotube in shape memory segmented fiber prepared by in situ polymerization and melt spinning’, Composites Part A: Applied Science and Manufacturing, 39(2), 314–321.
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Meng Q and Hu J (2008b), ‘A temperature-regulating fiber made of PEG-based smart copolymer’, Solar Energy Materials and Solar Cells, 92, 1245–1252. Nakayama K (1990), ‘Properties and application of shape memory polymer’, Nippon Gomu Kyokaishi, 63(9), 529–534. Ohki T, Ni Q-Q, Ohsako N and Iwamoto M (2004), ‘Mechanical and shape memory behavior of composites with shape memory polymer’, Composites Part A: Applied Science and Manufacturing, 35, 1065. Otsuka K and Wayman C M (1998), Shape Memory Materials, Cambridge University Press, Cambridge, UK. Paik I H, Goo N S, Jung Y C and Cho J W (2006), ‘Development and application of conducting shape memory polyurethane actuators’, Smart Mater. Struct., 15(5), 1476–1482. Ping P, Wang W, Chen X and Jing X (2005), ‘Poly(1-caprolactone) polyurethane and its Shape memory property’, Biomacromolecules, 6, 58. Ratna D and Karger-Kocsis J (2008), ‘Recent advances in shape memory polymers and composites: a review’, J. Mater. Sci., 43, 254–269. Schmidt A M (2006), ‘Electromagnetic activation of shape memory polymer networks containing magnetic nanoparticles’, Macromol. Rapid Commun., 27(14), 1168– 1172. Seok J H, Woong R Y, Ji H Y and Yang R C (2007), ‘Constitutive modeling of shape memory fibers and its application’, 5 September 2007, http://dspace.lib.fcu.edu.tw/ bitstream/2377/3946/1/ce05atc902007000069.pdf Shim Y S, Chun B C and Chung Y-C (2006), Fibers and Polymers, 7(4), 328. Sokolowski W, Metcalfe A and Hayashi S (2007), ‘Medical applications of shape memory polymers’, Biomed. Mater., 2, S23–S27. Stylios G K and Wan T Y (2007), ‘Shape memory training for smart fabrics’, Transactions of the Institute of Measurement and Control, 29(3–4), 321–336. Takahashi T, Hayashi N and Hayashi S (1996), ‘Structure and properties of shape-memory polyurethane block copolymers’, J. Appl. Polym. Sci., 60, 1061–1069. Tao X M (2001), Smart Fibres, Fabrics and Clothing, Woodhead Publishing, Cambridge, UK. Tobushi H, Hashimoto T, Ito N, Hayashi S and Yamada E (1998), ‘Shape fixity and shape recovery in a film of shape memory polymer of polyurethane series’, Journal of Intelligent Material Systems and Structures, 9(2), 127–136. Walker M (1983), ‘A system analysis of alternative concept for aircrew cold weather clothing’, Report no. NatickITr–841045, 35 pp. Wei Z G, Sandstrom R and Miyazaki S (1998), ‘Review: shape memory materials and hybrid composites for smart systems. Part I. Shape memory materials’, J. Mater. Sci., 33, 3743–3762. Xu B and Cuminato D F (1998), ‘Evaluating fabric smoothness appearance with a laser profilometer’, Textile Res. J., 68(12), 900–906. Zhu Y, Hu J, Yeung L-Y, Liu Y, Ji F L and Yeung K-w (2006), ‘Development of shape memory polyurethane fiber with complete shape recoverability’, Smart Mater. Struct., 15, 1385–1394.
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Plasma-treated yarns for biomedical applications
B. G u p t a, S. S a x e n a, N. G r o v e r, and A. R. R a y, Indian Institute of Technology, Delhi, India
Abstract: Surface modification by plasma treatment is achieved using different gases such as air, oxygen, nitrogen, argon and helium. The objectives of plasma surface modification in biomedical applications are adhesion promotion, enhanced surface wettability and spreading and reduced surface friction. In this chapter, we begin with a brief theory of the chemistry of plasma processing with the emphasis on plasma activation, grafting and plasma polymerization. The interaction mechanisms between polymeric surface and plasma are also examined. The resulting four main effects, namely cleaning ablation, crosslinking and surface modification which depends upon various parameters controlled by the operator, are also discussed. The effects of these plasma processes in biotextile engineering are also overviewed. Key words: plasma, grafting, biomaterial, medical textile, tissue enginnering, immobilizaton, suture, polymerization.
14.1
Introduction
Textile materials continue to serve an important function in the development of a wide range of medical and surgical products. Medical textiles are the products and constructions used as healthcare systems such as for first aid, clinical, hygiene implants and sutures covering a huge medical market. The demand for the biomedical textile market has been growing worldwide at an annual rate of 4.6% because of its innovative features [1,2]. The Indian market for medical textiles, currently worth around US$500 million, is witnessing robust growth of about 10–12% a year (Table 14.1). However, as compared with the global market of US$8238 million, the Indian market size is still very small [3]. Textile materials offer porosity and compliance which are often not exerted by other polymeric materials. Textile materials and products that have been engineered to meet particular needs are suitable for any medical and surgical application where a combination of strength, flexibility, and sometimes moisture and air permeability are very much required. Different forms of textile materials are used, including monofilament and multifilament yarns, woven, knitted, nonwoven fabrics, and composite structures. The number of applications is huge and diverse, 452 © Woodhead Publishing Limited, 2010
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Table 14.1 Medical textile market in India [3] Medical textile
Market size
Annual growth rate (%)
Surgical dressings healthcare textiles sutures Sanitary napkins Diapers Medical implants and devices
US$154.43 million US$26.72 million US$98 million – US$17.4 million US$4.2 million
5–10 13–16 15–20 8–10 5–10 10–15
ranging from a single thread suture to the complex composite structures for bone replacement, and from the simple cleaning wipe to the advanced barrier fabrics used in operation theatres. Textile structures are particularly attractive to tissue engineering because of their ability to tailor a broad spectrum of scaffolds with a wide range of properties. Today, one tries to promote the replacement of an injured tissue or organ by a new but identical tissue. Now the implants have to act as housing and a scaffold rather than a selfsufficient artificial organ. The body’s own cells are the main actors. There is no universal scaffold that meets the requirements of the various tissues of the human body. Furthermore, systematic study is necessary to design an optimal scaffold for each tissue application. The recent advances include the development of polylactic acid and polyglycolic acid fibres as structures for cell growth, temporary bioresorbable textile supports for growing human organic tissue, such as bladder reconstruction, tissue engineering of vascular grafts, etc. Surgical implantation of these materials is encountered with both thrombosis and inflammation at the site of injury. These processes are related, and both contribute to the healing of tissue into and around the material. Therefore, the main requirement for textile materials is bioreceptivity and biocompatibility along with the functional performance at the application site in human beings. For this requirement, it is necessary to modify the materials before use in biomedical engineering. The various approaches to develop functional biotextiles are blending, coating, chemical treatments, and graft polymerization for making the surface bioreceptive and biocompatible [4]. However, in most cases the inherent features of the biomaterials are affected due to the bulk modification. This is where one needs to modify the surface in such a way that the bulk remains intact. Plasma technology is widely used to alter the surface properties of polymers without affecting their bulk properties. The treated polymers have found various applications in automobiles, microelectronics, biomedical and chemical industries. Specific surface properties like hydrophobicity, chemical structures, roughness, conductivity, etc., can be modified to meet the specific requirements of these applications [5,6]. A wide range of surface modifications can be realized with different low-pressure plasmas. Hence, plasma surface modification has been employed in many technological fields, such as
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lubrication surfaces, bio-absorbable polymer, biocompatibility enhancement, bone internal fixation devices, diagnostic biosensors, etc. [7–13]. Recently, the application of plasma polymer as biomaterials has attracted the interest of many researchers [14–16]. The field of biomedical applications needs polymers which, besides satisfying the physical requirements of their application, show the so-called ‘biocompatibility’ with the biological environment in which they are employed. Since biocompatibility involves reactions of the interface of the device and the biological environment, surface modification techniques can be of great help in solving this problem, avoiding costly changes of materials. Among those techniques of surface modification, ‘cold’ plasma deserves an important place thanks to its characteristics [7,17]. For example, in many application fields, low molecular weight glycols have been utilized as feed gases in the radio frequency (rf) plasma, where they give rise to a PEO-like surface with non-fouling properties [18,19]. Non-fouling properties have been tested successfully for blood proteins (fibrinogen and albumin), for antibodies, cells and bacteria [20,21]. It is known that heparin and heparin-like molecules, collagen, albumin and other molecules of biological origin confer anti-thrombosis properties on polymer surfaces where they are immobilized [19–24]. The most frequently grafted groups are –NH2, –OH and –COOH, by means of RF glow discharges fed with non-depositing gases such as NH3, O2 and H2O. Such treatments are known to increase the usually low wettability of conventional polymers, and are utilized also to improve adhesion and the growth of cells on polymers [25–27]. The interface properties are analysed using the most important fluids implicated in the interfacial events related to the coagulation process at the interface of the blood–polymer surface. The interaction between the plasma and the polymer leads to two competing reactions – modification and degradation. When the modification effect dominates, the properties of the biomaterial will change due to the ion beam interaction. When degradation is prominent, etching will take place on the polymer surface. Two types of degradation reactions occur, namely chain scission and crosslinking. In most polymers, both have a place, but one is always predominant over the other. Polymers having a repeating unit of –CH2–CHR– undergo mainly crosslinking and low molecular weight products are formed; those with –CH2–CHRR¢– undergo chain scission reactions. The term ‘plasma’ was first used by Irving Langmuir in 1926 to describe the inner region of an electrical discharge. Later, the definition was broadened to define a state of matter in which a significant number of atoms and/or molecules are electrically charged or ionized. The component present will include ions, free electrons, photons, neutral atoms and molecules in ground and excited states and there is a high likelihood of surface interaction with organic substrates [28]. Plasma–polymer interaction is a multistage and multichannel process. This is caused by the variety of active species generated in plasma. At the same
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time, the depth of all these active species’ penetration into polymers does not exceed several micrometres (Table 14.2). Therefore, any application of the plasma treatment can be connected with the modification of the surface properties only [29]. The textile industry is searching for innovative production techniques to improve product quality, and in addition society requires new finishing techniques that respect the environment. Plasma surface treatments show distinct advantages, because they are able to modify the surface properties of inert materials, sometimes with environmentally friendly devices. On textile surfaces, three main effects can be obtained, depending on the treatment conditions: the cleaning effect, the increase of microroughness (anti-pilling finishing of wool) and the production of radicals to obtain hydrophilic or hydrophobic surfaces via plasma polymerization or graft polymerization. The choice of materials for various biomedical applications depends on their surface properties. All materials do not possess the surface properties required for biomedical applications. Surface properties of materials like surface free energy, hydrophilicity and surface morphology, which influence the cell–polymer interaction, decide the choice of the polymer. Plasma treatment of polymers can render the material surface either hydrophilic or hydrophobic through the use of the respective plasma gases. This process results in a smooth, pinhole-free ultrathin film. The major effects observed in plasma treatment of polymer surfaces are cleaning of organic contamination, micro-etching, crosslinking and surface chemistry modification [5,6]. Estimation of the influence of separate parameters on the results of surface modification by plasma etching has shown that the discharge current and treatment time are the most important factors. The influence of gas pressure and flow rate is not so significant [28]. The temperature, discharge power, pressure and oscillation frequency can vary in an extremely wide range. The contents of the plasma atmosphere (free electrons, radicals, ions, UV radiation and many different excited particles) depend on the type of gas used. The experiments show the surface properties attained by plasma action to be partially reversible. Probably, this is caused by a number of factors including the adsorption phenomena, relaxation of non-stable active sites and surface charge, and processes connected with the mobility of the Table 14.2 Mean depth of plasma active species action in polymers [6] Active species of Energy(eV) cold plasma Atoms, radicals, excited molecules Ions, electrons UV-photons
Mean depth of active species action
kT ª 0.01–0.1; E ª 0.5
>0.1 mm
1–100 5–20
Up to 10 monolayer Up to 10 mm
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macromolecule segments. This segment mobility leads to the removal of the plasma-formed functional groups from the superficial layer into the polymer volume. Aqueous and thermal treatments influence the stability of plasmainduced effects [29]. Plasma treatments involve the treatment of polymeric surfaces under different gaseous environments, such as oxygen, nitrogen or carbon dioxide (chemically reactive gases) or hydrogen, argon, helium and fluorinated gases (inert gases) for applications in adhesion improvement and in composites [30–39]. The former leads to the disruption of the polymer chains by the energetic ions and radiation generated in the plasma as well as to the introduction of chemical functional groups on the polymer surface, whereas the chemical effect is absent when inert gases are employed and only ion bombardment and radiation should in principle play a key role [39]. In order to develop plasma techniques on an industrial scale, the surface modifications should be stable with time. The ageing effect can be slowed down if a more cohesive and dense layer is obtained between the uppermost surface and the bulk material. Plasma, mainly generated by an electric field, could also be generated by other means, including a magnetic field, combustion and nuclear reactions. In an electric discharge, when an exciting field and a medium are coupled, plasma is generated. The quality of coupling determines the character of the electrical discharge [40]. The various kinds of reactions in the plasma include excitation, ionization and dissociation. The excitation process involves increase of translational energy and transition of internal energy to a higher state. Metastable atoms that collide with other atoms or molecules have a relatively long lifetime of about 10–3 s or more. Table 14.3 shows the metastable levels of several atoms and their lifetimes [41]. Plasma generated in a vacuum environment influences the surface of the polymer to make it suitable for a specific application. It has sufficiently high energy to break the covalent bonds of polymers exposed to the plasma. The surface of a biomaterial is what the body encounters first when a new device is used or implanted. In the case of polymers, the surface should be compatible with the biological system, which can be effectively modified by the plasma. Plasma treatment can improve wettability, oxidize the surface and enhance cell growth and adhesion [42]. Electron impact dissociation of gases plays an important role Table 14.3 Properties of metastable atoms [41] Atom Metastable state He Ar H N O
3
1
2 S1, 2 S0 43P2, 43P0 22S1/2 22D5/2, 22D3/2, 22P3/2, 22P1/2 21D2, 21S0, 35S2
Energy (eV)
Lifetime (s)
19.82, 20.61 11.55, 11.72 10.20 2.38, 2.38, 3.58, 3.58 1.96, 4.17, 9.13
6 ¥ 10–5, 2 ¥ 10–2 55.9, 44.9 0.12 6.3 ¥ 104, 1.4 ¥ 105, 13, 13 1.1 ¥ 102, 8.8 ¥ 10–1
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in the chemistry of low-pressure reactive discharges. Dissociation occurs as a result of inelastic collision of a molecule with an electron, ion or photon. When neutral fragments, either hot or in an excited state that are generated by this process, hit the substrate surface they affect the process chemistry [28].
14.2
Chemistry of plasma processing
Surface modification by plasma treatment is achieved using gases such as air, oxygen, nitrogen, argon and helium. The objectives of plasma surface modification in biomedical applications are adhesion promotion, enhanced surface wettability and spreading and reduced surface friction. Factors that contribute to improved adhesion are removal of surface contaminants and weakly bound polymer layers, and etching and substitution of chemical groups on the surface that permit covalent bonding [6], for example helium/ oxygen plasma treatment of polypropylene (PP) introduces oxidized functional groups onto the surface, which may include alcohol, ketone, carboxy, ether, ester or hydroperoxide. The introduction of polar groups onto the PP fibres allows chemical bonding with, for example, dye molecules, in contrast to the untreated PP molecular chains which are non-polar, giving a hydrophobic surface. Treatment of PTFE with hydrogen-containing plasmas such as forming gas (N2/H2: 95%/5%) and ammonia result in a large increase in the surface energy due to a high defluorination rate resulting in the formation of C–C, C–H and C==C bonds and crosslinks, and to nitrogen and oxygen species grafted onto the treated surface [43]. The introduction of functional groups on the polymeric surface mainly depends upon the type of gases used in the plasma; for example, oxygen and oxygen-containing plasmas impart functional groups such as –C–O, –C==O, –O–C==O and –C–O–O, as well as surface etching of fibres, all enhancing wettability and adhesion characteristics. Fluorine and fluorine-containing gases (CF4, C2F6) result in the incorporation of fluorine into the surface, resulting in hydrophobicity. Nitrogen and ammonia plasmas introduce amino (–NH2) and other nitrogencontaining functionalities.
14.2.1 Plasma activation Plasma activation is carried out with the intent to alter or improve adhesion properties of surfaces, for biosensors, tissue growth on polymeric surfaces [44–47], etc. In most cases, the surface in question is the surface of a polymer material and weakly ionized oxygen/ammonia plasma is used, which is widely used for treatment of polymeric surfaces for biomedical application. For example, it has been shown that oxygen plasma-treated bioabsorbable 3D PLA scaffold has better ability to house endothelial cells and improves
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cell adhesion, proliferation and migration in comparison to virgin scaffold [47], and anhydrous ammonia plasma treatment was used to modify surface properties to improve the human fibroblast cell affinity of the PLGA (70:30) scaffolds. The results show that hydrophilicity and surface energy were improved. Polar N-containing groups and positively charged groups were also incorporated into the sample surface [48]. A list of gases used in plasma processing, including polymerization, is provided in Table 14.4. Surface activation is a result of the removal of weak boundary layers. Plasma removes surface layers with the lowest molecular weight, at the same time oxidizing the uppermost atomic layer of the polymer and crosslinking of surface molecules. Oxygen radicals (and UV radiation, if present) help break up bonds and promote the three-dimensional cross-bonding of molecules and generation of polar groups. Oxidation of the polymer is responsible for the increase in polar groups which is directly related to the adhesion properties of the polymer surface. Alteration of surface characteristics is also possible by substitution of chemical groups present on the polymer chain being modified [49,50]. Different process gases can incorporate large varieties of chemical groups such as hydroxyl, carbonyl, carboxylic, amino or peroxyl groups. Oxidation, nitration, hydrolysation and amination processes induced by plasma are used to improve the surface energy of the substrate. Substituting the functional groups increases the surface energy and reactivity. The gases used to generate plasma are reactive, unlike in plasma-induced grafting [5]. For example, amine functionalities have been introduced onto the surface of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) by applying Table 14.4 Plasma gases and their applications [41] Plasma gas
Application
Oxidizing gases (O2, air, H2O, N2O) Removal of organics by oxidation and to leave oxygen species in the polymer surface Reducing gases (H2, mixtures of H2) Replacement of F or O in surfaces, removal of oxidation sensitive materials, conversion of contaminants to low molecular weight species that do not polymerize or re-deposit on adjacent surfaces Noble gases (Ar, He)
To generate free radicals in surfaces to cause crosslinking or to generate active sites for further reaction
Active gases (NH3)
To generate amino groups
Fluorinated gases (CF4, SF6 and other perfluorinated gases)
To make the surface inert and hydrophobic
Polymerizing gases (monomer gases for direct polymerization, Ar or He pretreated)
Polymerization of layers onto substrates by direct polymerization by grafting on Ar or He pretreated polymer surface
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radio frequency ammonia plasma treatment and wet ethylenediamine (ED) treatment. It was found that ammonia plasma gave a larger amount of amino groups on the surface as assessed by X-ray photoelectron spectroscopy after trifluoromethylbenzaldehyde (TFBA) derivatization (Fig. 14.1). The ED aminolysis method was considered less advantageous as the modified surfaces suffered from degradation and an increase in crystallinity during storage. The spatial distribution of the amino groups found by Raman mapping on the substrates treated by the two methods was patchy and uneven [51]. Apart from hydrophilicity and surface chemistry, surface roughness can also influence cell spreading and growth [52]. Surface roughness activates different types of cells to respond in different ways [53]. Plasma treatment causes physical and chemical changes, which include crosslinking of the near surface volume, polymer degradation, ablation (etching) and the formation of free radicals [54]. The influence of a plasma composition atmosphere on the surface characteristic of a polyester fabric has been investigated after being treated with plasma, with emphasis on the wettability. Thus, a fabric that is 100% polyester was treated inside an experimental reactor, varying the composition and concentration of the gases that originated the plasma, but maintaining constant the other parameters (pressure, temperature, current, voltage and exposure time). The plasma treatment was very efficient at improving the wettability of a polyester fabric. The water absorption in 60 s was eight times higher, and in 200 s it was 12 times higher, than the water absorption of the non-treated fabric. The best wettability result was obtained by using an atmosphere of O10N83H7 (10% O2, 83% N2 and 7% H2). There was no formation of new chemical groups on the fibre surface, especially –OH and –NH2 which were desired. The plasma particles attacked originated fissures and pores on the fibre surface, which caused an increase in wettability of the treated fabric. It was shown that air plasma was more efficient in incorporating oxygen functionalities than argon plasma, which was more efficient than helium plasma. The polyethylene terephthalate (PET) and polypropylene (PP) non-wovens, modified in air, helium and argon, showed a significant increase in liquid absorptive capacity due to the incorporation of oxygen-containing groups, such as –C–O, –O–C==O and –C==O. The CF3 CF3
NH2 +
N
O
14.1 Reaction scheme for TFBA derivatization of amine functionalities [53].
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ageing behaviour of the plasma-treated textiles after storage in air showed that the induced oxygen-containing groups reorientated into the bulk of the material. This ageing effect was the smallest for the argon-plasma treated non-wovens, followed by the helium-plasma treated non-wovens, while the air-plasma treated non-wovens showed the largest ageing effect [55]. The atomic composition of the saturated PP and PET non-wovens was investigated as a function of storage time. Figure 14.2(a) and (b) show the evolution of the O/C atomic ratio as a function of ageing time for the PP and PET non-wovens, respectively. During the ageing process, the O/C atomic ratio decreased with increasing ageing time, until a plateau value was reached. As can be seen in Fig. 14.2(a), the O/C atomic ratio of the PP non-woven decreased from 17.7% immediately after plasma treatment to 11.6% for an air-plasma treated PP non-woven, 13.3% for a helium-plasma treated PP non-woven and 13.8% for an argon-plasma treated PP non-woven after 48 hours of storage. Figure 14.2(b) shows that the O/C atomic ratio of the PET non-woven decreased from 47.4% immediately after treatment to 34.5% for an air-plasma treated PET non-woven, 36.6% for a helium-plasma treated PET non-woven and 38.2% for an argon-plasma treated PET non-woven. Figure 14.2 also shows that during the first hours of storage, the decrease in O/C atomic ratio was the largest for textiles treated with air plasma and the smallest for textiles treated with argon plasma. The optimum plateau value of the O/C atomic ratio also depended on the working gas used during plasma treatment. The plateau value was the highest for the argon-plasma treated textiles and the lowest for the air-plasma treated textiles. Important to mention is the fact that the plateau values of the O/C ratios after ageing were considerably higher than the O/C ratios of the untreated textile samples. This meant that the polymer surfaces never completely recovered, since a 18
50 46 O/C ratio (%)
14
O/C ratio (%)
Argon Helium Air Untreated
42
10
Argon Helium Air Untreated
6 2
0
10
20 30 40 Ageing time (h) (a)
38 34
50
30 0
10
20 30 40 Ageing time (h) (b)
50
14.2 Evolution of the O/C atomic ratio as a function of ageing time for (a) the plasma-treated PP non-wovens and (b) the plasma-treated PET non-wovens [57].
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certain oxygen concentration, induced after plasma treatment, remained on the surface [55]. Plasma treatment can also have profound effects on the surface properties of nanofibres by changing their surface physical and chemical features [56]. The modification of polymer nanofibre surface by plasma treatment has great potential for nanofibres in such applications as biomaterials, sensors and medical devices. The influence of atmospheric pressure plasma treatment time on penetration depth of surface modification into PET fabric has also been studied and it has been predicted that the maximum penetration depth was six layers of fabrics with reasonable treatment duration [57]. The change in surface morphology, mainly rms surface roughness and surface area, on the PET fabrics surface due to air cold plasma have also been measured as a function of treatment time and as a function of gas pressure. The same quantities as a function of pressure were measured also for He, Ar, SF6 and CF4 gases (Table 14.5). The changes in morphology in the cases of air, He and Ar gases seem to be due mainly to etching effects. The situation is different for SF6 and CF4 gases where reorganization of the surface, possibly due to fluorine atoms grafting, seems to be effective [58].
14.2.2 Plasma grafting Plasma-induced graft polymerization is an attractive way of modifying surface chemistry and morphology of polymeric materials [59–63]. A Table 14.5 The rms surface roughness and surface area data, as mean value of 15 AFM images, of PET textile samples for the studied pressures and plasma gases [60] Rms (nm)
Surface area (µm2)
Untreated
20.2 ± 4.7
1.34 ± 0.18
Air
0.1 0.2 0.4
39.7 ± 8.1 43.3 ± 8.2 48.2 ± 8.4
2.55 ± 0.39 3.41 ± 0.74 4.28 ± 1.01
He
0.4 0.8
37.9 ± 8.4 46.1 ± 10.2
2.85 ± 0.43 3.32 ± 0.81
Ar
0.05 0.2 0.4
65.9 ± 9.6 77.7 ± 9.8 83.1 ± 10.3
5.85 ± 1.35 7.29 ± 1.63 7.98 ± 1.81
SF6
0.05 0.2 0.4
32.2 ± 7.1 26.6 ± 6.7 24.9 ± 5.2
2.25 ± 0.72 2.08 ± 0.50 2.05 ± 0.41
CF4
0.07 0.2 0.4
37.8 ± 7.1 35.7 ± 7.1 28.9 ± 6.0
2.47 ± 0.41 2.32 ± 0.52 2.13 ± 0.39
Gas
Pressure (mbar)
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desired monomer may be polymerized onto the surface of a plasma-activated polymer, resulting in the formation of a grafted brush layer on top of the surface. The grafted surfaces may then provide active sites for the binding of biomolecules or antimicrobial drugs. Therefore, it is necessary to modify the polymeric surface to make it bioreceptive for its application as biomaterial. Plasma-induced graft polymerization has consequently proven highly successful as a means to develop functional interfaces for the immobilization of biomolecules and apt for the culture [64–70]. During recent decades, a large number of investigations have been undertaken to develop biomedical materials which do not elicit thrombus formation when exposed to flowing blood. However, no thrombo-resistant material that is reliable for long-term use has been reported, because many parameters govern platelet aggregation and blood coagulation. Among them are surface properties of the material and the hydrodynamic conditions of flowing blood. Hydrophilic crosslinked gels have recently attracted considerable attention as candidates for good biocompatible materials, because the interface between the water-swollen gel and blood or tissues may have a very low free energy, leading to very low adverse interaction of the gel surface with the aqueous biological environment [71]. Therefore, the grafting of hydrophilic monomers, such as acrylic acid (AA) or methacrylic acid (MAA), leads to a surface with suitable chemical functionality for biomolecule interaction at the interface. Graft polymerization of acrylic acid onto polyethylene terepthalate (PET) monofilament has been carried out using oxygen plasma to activate the PET surface for graft polymerization of acrylic acid and chitosan immobilization [72]. The filament was pretreated with oxygen plasma for introduction of peroxides and subsequently grafted with acrylic acid. The influence of monomer concentration, plasma exposure time and reaction temperature on the degree of grafting was investigated. The grafted filament was subsequently immobilized with chitosan to make it antimicrobial for using as a suture application. Since microbial infection on the implanted site has often been observed to lead to deterioration of the wound and related complications, the development of the antimicrobial suture may provide the necessary environment for an infection-free healing process. The key requirement of a development process is that the modification of polypropylene (PP) or PET sutures should be carried out in such a way that it acquires functional groups where a drug may be immobilized. This drug is released from the suture once in contact with the biosystem and provides antimicrobial action at the stitch site. The oxygen plasma exposure of PP or PET monofilament leads to the formation of hydroperoxides and peroxides. These hydroperoxides and peroxides are thermally labile functional groups and undergo decomposition and initiate graft polymerization of acrylic acid to create polyacrylic acid brushes on the polymer surface [73]. The influence of the reaction temperature on the degree of grafting is
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shown in Fig. 14.3. The grafting was carried out from 50° to 80°C at a 40% monomer concentration. The equilibrium of the degree of grafting increased up to 60°C and thereafter tended to decrease. It is proposed that in the early stages of the reaction, homopolymer formation was very limited, which was separated by non-solvent MEK, and the local stationary concentration of monomer around the growing chain was maintained. This ensures fast initiation and propagation. However, with increasing temperature, the concentration of propagating chains is increased because of a higher peroxide decomposition rate, and the termination of two growing chains by mutual recombination becomes a major factor. Once the homopolymer formation is extensive, the monomer depletion favours more chain transfer in the system. It is possible that the chain transfer steps (at temperatures higher than 60°C) dominated to such an extent that the degree of grafting was reduced. It may also be possible that some of the primary radicals (PO•) become deactivated in the reaction medium, contributing to the reduced degree of grafting at higher temperatures. The glass transition temperature seems to be an important factor in the observed behaviour of the reaction temperature [72]. The surface topography of filaments was observed by AFM (Fig. 14.4). The surface roughness increased due to the grafting of acrylic acid. This is because poly(acrylic acid) chains form their own domains and morphology at the surface, giving a characteristic hill–valley structure. When chitosan is immobilized onto the grafted surface, it fills the valleys and leads to the flattening of the surface. The RMS value of roughness clearly reflects this behaviour (Fig. 14.5) [72].
Degree of grafting (mg/cm2)
25
20
15
10
5
0 40
50
60 70 Temperature (°C)
80
90
14.3 Influence of reaction temperature on the degree of grafting. Reaction conditions: plasma exposure time, 180 s; plasma power, 100 W; MEK, 60%; monomer, 40%; reaction time, 6 h [74].
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(a) Virgin PET
(b) PET-g-AA
(c) PET-g-AA-CS
14.4 AFM images of (a) virgin, (b) acrylic acid grafted (10.5 mm/cm2), and (c) chitosan immobilized PET monofilaments [74].
60 50
RMS roughness (Å)
464
40
30
20
10
0
Virgin PET
PET-g-AA
PET-g-AA-CS
14.5 RMS values of roughness of virgin, acrylic acid grafted (10.5 mm/ cm2), and chitosan immobilized PET monofilaments [74].
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The influence of the reaction medium on the degree of grafting has also been investigated by the plasma-induced graft polymerization of acrylic acid onto PP monofilament. The graft management on the filament surface is strongly influenced by the reaction conditions employed at any stage. The variation of the degree of grafting with ferrous sulfate concentration is presented in Fig. 14.6. It is important to mention that no grafting takes place in the absence of an added inhibitor, since homopolymerization is so intense that hardly any monomer is left behind for the grafting reaction to take place [73]. In the presence of ferrous sulfate as inhibitor, a reasonable amount of grafting takes place. However, as the ferrous sulfate concentration increases the grafting increases initially, reaches its maximum and then decreases fast. The homopolymer formation is also inhibited as the ferrous sulfate concentration increases. Virtually no homopolymer formation takes place at the ferrous sulfate concentration of 0.06%. The initial increase in the grafting is because of the diminishing homopolymerization with the increasing ferrous sulfate concentration so that sufficient monomer remains available for the grafting reaction. The maximum grafting is achieved at 0.06% ferrous sulfate concentration, beyond which a drastic reduction of the degree of grafting occurs. It may be stated that in spite of free monomer availability for grafting, the ferrous sulfate not only hinders the homopolymerization by deactivating the hydroxyl radical into hydroxyl anion but also deactivates the primary PO∑ radicals as well as propagating polyacrylic acid chains leading to very little degree of grafting. These observations show that the use of
Degree of grafting (mg/cm2)
[M] : 30% T : 59°C Time : 2.5 h
8
80
6
60
4
40
2
20
0
0.05
0.10
0.15 FeSO4 (%)
0.20
Homopolymerization (%)
100
10
0 0.25
14.6 Variation of the degree of grafting and of homopolymerization with ferrous sulfate concentration. Plasma treatment conditions: exposure time, 60 s; plasma power, 60 W; O2 pressure, 20 sccm [75].
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ferrous sulfate in the grafting medium is bound to produce material with a low level of grafts on the PP surface. To replace ferrous sulfate by organic additives, different solvents were added to the grafting medium and a precise monitoring of homopolymerization was carried out. A comparative investigation on the addition of methanol, acetone and butanone on the degree of grafting is presented in Fig. 14.7. A maximum of 42 mg/cm2 graft level was achieved for the acetone addition under our experimental conditions. All additives are able to inhibit the homopolymer formation during the grafting reaction as represented by the bar on each plot beyond which the reactions tend to be homopolymer free. The homopolymer formation has always been higher in acetone medium as compared to methanol. For example at 40% solvent addition, the homopolymer is 3.5% as compared to 0.6% in methanol. Although the homopolymer yield seems to be low, the viscosity of the grafting medium will be highly affected because of the hydrogel nature of acrylic acid. Acetone and methanol show almost identical trends in the graft variation with their content in the grafting medium. The grafting increases with the additive content, reaches a maximum at 40% and then tends to decrease. The favourable aspect is that the inhibitory action of methanol and acetone helps in maintaining sufficient monomer accessibility to the grafting reaction. It seems that the inhibitory action of both the additives on the one hand helps in homopolymer inhibition, and on the other hand deactivates a fraction of the growing polyacrylic acid chains and is reflected in the form of a decrease in the degree of grafting.
Degree of grafting (mg/cm2)
50
40
Acetone Methanol Butanone
30
20
10
0
20 40 60 80 Organic in water–orgaic mixture (%)
100
14.7 Variation of the degree of grafting with the water-organic composition. Plasma treatment conditions: exposure time, 60 s; plasma power, 60 W; O2 pressure, 20 sccm. Grafting conditions: monomer concentration, 30%; temperature, 50∞C; time, 2.5 h [75].
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The addition of butanone shows the grafting trend to be similar to that of the methanol and acetone but with a maximum at 60% concentration. It is observed that the homopolymerization is completely inhibited beyond 60% butanone content. The degree of grafting is much lower than that obtained for acetone and methanol addition. Unlike methanol and acetone, butanone acts as the non-solvent for the growing polyacrylic acid chains. This precipitates out the polyacrylic acid as soon as it is formed in the reaction medium. As a result, the viscosity of the grafting medium is considerably maintained. In spite of the fact that this regulates the monomer diffusion to the grafting sites for a smooth grafting reaction, the degree of grafting is much lower. This may be due to the non-solvent nature of butanone towards polyacrylic acid chains: the grafted layer on the PP surface does not swell and the enrichment of the grafted layer with monomer does not proceed well. As a result, termination of the growing chain follows instantaneously, providing low graft levels. These observations on the inhibitory influence of the organic additives acetone, methanol and butanone are interesting in achieving a homopolymer-free grafting reaction. It is difficult to predict any precise mechanism for these observations [73].
14.2.3 Plasma polymerization Plasma polymerization uses plasma sources to generate a gas discharge that provides energy to activate or fragment gaseous or liquid monomer, often containing a vinyl group, in order to initiate polymerization. Plasma polymerization can be used to deposit polymer thin films. By selecting the monomer type and the energy density per monomer, known as the Yasuda parameter, the chemical composition and structure of the resulting thin film can be varied in a wide range. Plasma polymerization takes place in a low pressure and low temperature plasma that is produced by a glow discharge through an organic gas or vapour. Plasma polymerization depends on monomer flow rate, system pressure and discharge power among other variable parameters such as the geometry of the system, the reactivity of the starting monomer, the frequency of the excitation signal and the temperature of the substrate. A more general description was given by Yasuda [74] who identified two regimes of plasma polymerization in which the mechanisms differ dramatically, i.e. the monomer-deficient and the energy-deficient plasma. Indeed the composite plasma process parameter W/FM (where W is the discharge power and FM is the mass flow rate of monomer) has been shown to be very efficient in controlling the chemical structure of the polymer. In fact, at a relatively low input energy level (energy-deficient region) a plasma polymer is obtained that is characterized by a chemical structure and properties similar to those of conventional polymers. The plasma polymerization process, which can
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produce thin films with unique chemical and physical properties, has found various biomedical applications [75–77]. In this process, gases in the plasma undergo polymerization through a free-radical initiation process. Methane, ethylene, propylene, fluorocarbon monomers and organosilicon compounds can be polymerized by this method. When the process gas mixture contains hydrocarbons, the hydrocarbon molecules are fractured into free-radical fragments. These free radicals initiate polymerization. As the molecular weight of the polymer increases, it is deposited on the surface of the substrate. Polymerization at an atomic level is also possible when sufficient energy is supplied to break all the bonds on the monomer. The plasma-polymerized thin films are generally pinhole-free, highly crosslinked and strongly bound to the surface [78,79]. Application of plasma-polymerized surfaces is associated with biomedical uses, e.g. immobilized enzymes [80,81], sterilization [82] and pasteurization [83], the textile industry [84], electronics (e.g., amorphous semiconductors [85]), electrics (insulators [86], thin film dielectrics [87]), optical applications [88,89], chemical processing (reverse osmosis membrane [90], permselective membrane [91]) and surface modification (adhesive improvement [92,93], protective coating [94,95]). For example, plasma polymerization may offer a new alternative in biosensor interface design. The advantage is that an extremely thin (<1 mm) film with good adhesion can be produced. Furthermore, the film is pinhole-free and both mechanically and chemically stable, and it allows a large amount of biological materials to be loaded onto the surface [96]. The manufacture of integrated transducer arrays is now possible by means of plasma technology. The techniques have actually been used to increase the dynamic range and sensitivity of urea sensors [97,98].
14.3
Biomedical applications
Plasma generated in a vacuum environment influences the surface of the polymer to make it suitable for a specific application. Plasma pretreatment is widely recognized as a clean and effective method [99]. In particular, low temperature plasma processing has been progressively applied to activate the outermost surface of a polymer without affecting its structural dimensions [100]. Both ionized species and free radicals in the reactive plasma play important roles in interacting with an organic surface by forming oxidative groups [101,102]. Plasma has sufficiently high energy to break the covalent bonds of polymers exposed to the plasma. The surface of a biomaterial is what the body encounters first when a new device is used or implanted. In the case of polymers, the surface should be compatible with the biological system, which can be effectively modified by the plasma. Plasma treatment can improve wettability, oxidize the surface and enhance cell growth and adhesion. The surface chemistry may be altered by proper selection of the
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nature of the gaseous medium. Gases such as oxygen, ammonia and carbon dioxide produce functionalities such as hydroperoxide, amino and carboxylic groups, respectively. However, inert gases such as argon lead to the formation of radical sites on the polymer backbone, which are transformed into polar functionality in the presence of oxygen. These functionalities act as the ‘anchoring sites’ for the attachment of the biological molecules [103]. The application areas vary from wound dressings and sutures to tissue engineering scaffolds and implants.
14.3.1 Wound dressings Wound healing is a complicated sequence of cellular and biochemical events that proceed through a series of different phases [104, 105]. Wound healing, or wound repair, is the body’s natural process of regenerating dermal and epidermal tissue. When an individual is wounded, a set of complex biochemical events takes place in a closely orchestrated cascade to repair the damage. These events overlap in time [106,107] and may be artificially categorized into separate steps: the inflammatory, proliferative, and remodelling phases [108]. In the inflammatory phase, bacteria and debris are phagocytized and removed, and factors are released that cause the migration and division of cells involved in the proliferative phase. The proliferative phase is characterized by angiogenesis, collagen deposition, granulation tissue formation, epithelialization, and wound contraction [109]. In angiogenesis, new blood vessels grow from endothelial cells. In fibroplasia and granulation tissue formation, fibroblasts grow and form a new, provisional extracellular matrix (ECM) by excreting collagen and fibronectin. In epithelialization, epithelial cells crawl across the wound bed to cover it. In contraction, the wound is made smaller by the action of myofibroblasts, which establish a grip on the wound edges and contract themselves using a mechanism similar to that in smooth muscle cells. When the cells’ roles are close to complete, unneeded cells undergo apoptosis. In the maturation and remodelling phase, collagen is remodelled and realigned along tension lines, and cells that are no longer needed are removed by apoptosis [109]. For the choice of proper biomaterials in wound dressing, the role of collagen at each phase of wound healing is well understood and appreciated [110]. Many collagen products for wound healing have been developed in the past few years [111–113]. The treatment of extensively burned patients is a difficult clinical problem not only because of the extent of the physiological abnormalities caused by the burn itself, but also because of the small area of normal skin available to cover the large injury area. Under the circumstance, the burn illness is greatly complicated by the persistence of a large, open wound which has to be closed promptly. So a tri-layer membrane as the artificial skin for extensive burn injury has been prepared using plasma
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surface modification by Lin et al. [114]. Polysaccharides, e.g. chitosan, having hydrogel-forming properties, have also been considered as wound dressing materials [115–117]. Chitosan is partially N-deacetylated chitin, and chitin is a linear homopolymer of 1,4-N-acetyl-d-glucosamine. Both chitin and chitosan have many useful and advantageous biological properties in application as a wound dressing, namely biocompatibility, biodegradability, haemostatic activity, anti-infectional activity, and ability to accelerate wound healing without scarring [117-119]. Polyethylene terephthalate (PET) is often used as a basic material in the textile industries, plastics industries and various biomedical fields such as suture, bandages, scaffolds, prosthesis, etc. Accordingly, improvement of the antibacterial properties of PETs is important for a wide range of industrial applications. PET texture was exposed to oxygen plasma glow discharge to produce peroxides on its surface. These peroxides were used as catalysts for the polymerization of acrylic acid (AA) in order to prepare a PET introduced by a carboxylic acid group (PET-A). chitosan and quaternized chitosan (QC) were then coupled with the carboxyl groups on the PET-A using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide to obtain chitosan-grafted PET (PET-A-C) and QC-grafted PET (PET-A-QC), respectively (Fig. 14.8) [120]. The proliferation of bacteria in a PBS solution can be influenced by the shaking speed of the cell suspension. Figure 14.9 shows the effect of the shaking speed of the bacteria suspension on growth inhibition. The growth inhibition of the cells decreased with an increase in the shaking speed. The growth of S. aureus was not much influenced by contact with PET or AAgrafted PET (Fig. 14.10). However, the growth of bacteria was significantly inhibited by contact with chitosan-grafted PET (62% in PET-A−–Cl+, 39% in PET-A-C, 59% in PET-A-QC). After 6 h of shaking the growth of bacteria was markedly inhibited by PET with ionically (86%) and covalently (75%) grafted chitosan and covalently grafted QC (83%). The PET-A−–Cl+ (86%) showed higher antibacterial activity than PET-A-C (75%). The high growth inhibition of the cells by PET-A−–Cl+ may have originated from the easy release of chitosan from the matrices. In PET-A−–Cl+ the chitosan were ionically bound to the carboxyl groups on the surfaces. As a result, these chitosan could be released from the PET surface during shaking in the flask, thereby inhibiting the bacterial growth in the medium. The high growth inhibition by PET-A-QC seems to be attributed to the quaternary ammonium ions of the grafted chitosan [120].
14.3.2 Antimicrobial treatment Microbial attack on textiles can be classified into two main categories: firstly, those that are detrimental to the consumer, such as odour formation and contamination; and secondly, those that affect the fabric itself, in terms
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of strength reduction and quality loss. Antimicrobials are defined as agents that either kill microorganisms (biocidal) or inhibit their growth (biostatic). The mechanisms by which they act include: ∑ ∑ ∑ ∑ ∑ ∑
Cell wall damage Alteration of cell wall permeability Inhibition of cell wall synthesis Inhibition of protein and nucleic acid synthesis Inhibition of enzyme action Inactivation of DNA.
An antimicrobial textile can act in two distinct ways – by contact and by diffusion. In the contact method, the antimicrobial agent is placed on the fibre and does not disperse, so it acts only when microorganisms touch the fibre. In the diffusion method, the antimicrobial agent is placed on the surface or in the fibre and then migrates more or less rapidly in a humid external medium to reach the microorganisms and inhibit their growth [121]. O4
O2 plasma 120 W, 0.2 torr, 30 s
OH
In air
O–O4
O–OH
Pet
OH 10% acrylic acid Sodium pyrosulfite
COOH
COOH O
COOH
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Pet-a
CH2
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CH
COOH
H
WSC Chitosan
O
CH2
CH
CH2
C=O N O
CH
H
COOH
Hm O
OH
OH
n·m O
OH O
Pet-a
OH Pet-a-C
m
NH2 X·m
14.8 Schematic diagram showing the formation of chitosan grafted poly(ethylene terephthalate) (PET-A-C) [122].
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Growth inhibition rate (%)
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14.9 Effect of shaking speed on bacteria growth inhibition in a flask [122].
Growth inhibition (%)
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80 60 40
20
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PET
PET-A
PET-A-C¢
PET-A-C PET-A-QC
14.10 Bacteria growth inhibition by surface modified PET after 1 h and 6 h of shaking [122].
Various different agents are used to give textiles antimicrobial properties, including metals and metal salts, mostly based on silver or copper [123,124], quarternary ammonium salts [125,126], N-halamines, which also enable a regeneratable finish [127,128], organic molecules (e.g. triclosan [129]), and natural substances (e.g. chitosan [130] or lysozyme [130]). Antibiotics may also be necessary, but, due to the possible formation of resistant strains, antibiotics should be used only for medical indications. Fabrication methods for antimicrobial textiles can be classified into two categories: the addition of an antimicrobial agent to the polymer before extrusion (intrinsically antimicrobial fibres), or post-treatment of the fibre or fabric during the
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finishing stages. Plasma-based treatments can be used to create antimicrobial coatings on textiles. Chitosan can be grafted onto plasma-functionalized polymer surfaces if carboxyl groups are generated. Hun et al. [131] describe the activation of PET with an oxygen plasma glow discharge treatment followed by wet chemical acrylic acid grafting and a subsequent reaction with chitosan. The poly(acrylic acid) can also be plasma polymerized on nearly all substrates using low power or pulsed plasmas [132]. A subsequent wet chemical treatment with silver nitrate produces silver carboxylated coatings, resulting in an antimicrobial finish due to the release of Ag+ ions [133]. The silver carboxylate can also be reduced at suitable pH with mild reducing agents to obtain silver clusters at the fabric surface [134]. In the medical field, for the past two decades medical fabrics are gaining importance as healthcare professionals and public health officials are mandating barriers against highly communicable bacteria and viruses. In the surgical zone it becomes very important to protect the surgical team from the patient’s infectious blood and other body fluids and vice versa. So the surgical fabrics should have more fluid repellency and antimicrobial properties [135,136]. Several researchers throughout the world have reported on the surface modification of the polymer substrate by low-temperature plasma treatment to make it antimicrobial [137–139]. The cotton fabric was subjected to RF air-plasma treatment to increase its hydrophilicity and was further treated with neem leaf extract (azadirachtin) to increase the antimicrobial activity to the cotton fabric. The process parameters were optimized to impart maximum hydrophilicity and are confirmed by the static immersion test. This increase in hydrophilicity is attributed to the formation of carbonyls on the fabric surface due to formation of cellulosic radicals and also due to a chemical reaction between these radicals and plasma particles. FTIR analysis reveals the presence of carbonyls. The plasma-treated cotton fabric was found to absorb more azadirachtin because of the increased polarity of the carbonyl group which enhances the antimicrobial efficacy and is evident from agar diffusion and modified Hohenstein test results (Fig. 14.11). The citric acid added as a crosslinking agent increases the durability of the finish by forming a chemical bond with both azadirachtin and the fabric, which is also evident from the FTIR spectra [140]. Vaideki et al. [139] have shown that the antimicrobial activity was increased when cotton fabric was treated with RF oxygen plasma and then treated with neem leaf extract (azadirachtin) to impart antimicrobial activity. The maximum absorption percentage of the sample due to RF oxygen plasma treatment was found for the exposure time of 10 min as shown in Fig. 14.12 and reveals the maximum antimicrobial activity that was obtained for the same sample when treated with neem extract. The antimicrobial activity of these samples was compared with the activity of the cotton fabric treated with neem extract alone. The investigation reveals that the surface modification
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14.11 FTIR spectrum of the cotton fabric treated with air plasma and the antimicrobial finish (azadirachtin and citric acid for crosslinking) [137]. 62 Electrode gap: 3 cm Oxygen pressure: 0.06 mbar
61
Absorbance (%)
60 59 58 57 56 55 54 0
5
10 15 Time of exposure (min)
20
25
14.12 Absorption percentage vs. time of exposure [141].
due to RF oxygen-plasma was found to increase the hydrophilicity and hence the antimicrobial activity of the cotton fabric when treated with azadirachtin (Fig. 14.13). Bioassay of the fabrics was carried out using several microorganisms. It was found that the native fabrics had no biocidal activity and the plasma-treated ones showed slight activity; however, the fabrics
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2
14.13 Zone of bacteriostasis of (1) RF oxygen plasma (optimized parameter) and (2) neem extract treated sample [141].
coated with chitosan and its derivatives showed much higher antifungal as well as antibacterial activity. The antimicrobial activity was found to depend on the type of organism and the type of chitosan derivative. In the present scenario, nanoscale materials have emerged as novel antimicrobial agents owing to their high surface area to volume ratio and their unique chemical and physical properties [141,142]. The great developments in synthesis of nanoparticles (NPs) and their numerous potential applications have opened up new possibilities for engineering the advanced properties of textile materials [143,144]. Various nanometre-sized metal and metal oxide particles can provide antibacterial properties, but silver NPs seem to be particularly attractive due to the excellent antimicrobial efficiency of silver that itself has been known for a long time [145–148]. The application of silver NPs in the antibacterial finishing of textiles is favourable due to their stability and high surface to volume ratio. Therefore, a considerable amount of the silver atoms on the surface of the NPs is exposed to the surrounding medium, providing significant bactericidal efficiency. The surfaces of polyester (PES) and polyamide (PA) fabrics were activated using corona treatment carried out at atmospheric pressure, which facilitated the loading of silver NPs from colloid onto the PES and PA fabrics to improve their antibacterial properties. Both fabrics showed excellent antibacterial effects against Gram-
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positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria and showed excellent laundering durability, but the antibacterial efficiencies of silver-loaded PA and particularly PES fabrics that had been previously activated by corona were more prominent for E. coli. [149].
14.3.3 Plasma sterilization Nowadays, plasma treatment is used for the sterilization of various materials. Sterilization is based on either a physical or a chemical process that destroys or eliminates microorganisms, or both [150,151]. Traditional methods for sterilization include autoclaving, dry heat, ethylene oxide (EG) gas, gamma ray and UV irradiation, which are reliable and well understood. However, all of these methods have their advantages as well as their disadvantages. Sterilization by plasma is an alternative method to the conventional sterilization methods [152]. Plasma treatment is a new sterilization method in the field of protection and conservation of materials from microorganisms. Moreover, microwave-induced argon plasma treatment has advantages, such as its sterilizing potential at a relatively low temperature, the possible preservation of the integrity of polymer-based materials and the biological safety compared to EO gas [153–155]. In addition, it is capable not only of killing bacteria and fungi, but also of removing the dead microbes (e.g., pyrogens) from the surface of the objects to be sterilized [156,157]. Park et al. [158] investigated the sterilization effects of microwave-induced argon plasma at atmospheric pressure on the microorganisms in silk fabrics. Also, they examined the influence of plasma treatment on the physical properties of the fabrics for longer-term conservation. The sterilization effects of microwave-induced argon plasma at atmospheric pressure on bacterial and fungal strains in silk fabrics are shown in Fig. 14.14. Although S. aureus was the most resistant bacterial strain to the plasma treatment, all the strains were completely sterilized in less than 7 s. The number of recovered colonies after plasma treatment was significantly decreased in a time-dependent manner. The sterilization effect of plasma treatment was confirmed by SEM micrographs showing the morphological alterations of the strains of P. aeruginosa and A. niger (Fig. 14.15) by plasma treatment for 5 s. The morphology of the untreated P. aeruginosa spores was a typically round shape with average diameter of 0.6 mm (Fig. 14.15(a,b). In contrast, the plasma-treated spores were completely destroyed with severely damaged and ruptured cell membranes (Fig. 14.15(c)). Moreover, the intracellular contents were all released into the surrounding surface after plasma treatment and the original shape and structure of spores disappeared with microscopic debris (Fig. 14.15(d)). Similarly plasma treatment also destroys A. niger by creating holes in its cell wall. It is well known that two combined mechanisms are involved in the plasma-mediated sterilization as follows: the destruction of
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7 P. aeruginosa S. aureus A. niger P. citrinum
6
Log (cfu/ml)
5 4 3 2 1 0
0
1
2 3 4 5 Plasma treatment time (s)
6
7
14.14 Sterilization effects of microwave-induced argon plasma treatment on silk fabrics inoculated with some kinds of bacterial and fungal strains [158].
cell wall and DNA by UV irradiation and activated free radicals, and the erosion of microorganisms through etching eventually enhanced by UV radiation [151,157,158]. The UV and activated free radicals generated during plasma treatment weaken the cell wall of the microorganisms by reacting with the hydrocarbon bonds and cause the disruption of unsaturated bonds, particularly the purine and pyrimidine components of the nucleoproteins. As the process continues, the plasma removes the outer cell wall layer of the microorganisms with its burst and destruction. Another sterilization process of microwave plasma is the erosion of the microorganisms through etching to form volatile compounds through slow combustion by oxygen atoms or radicals emanating from the plasma. It was also found that the plasma treatment did not affect the ultimate tensile strength and surface morphology of the fabrics, as shown in Fig. 14.16. The ultimate tensile strength of the fabrics was slightly decreased by plasma treatment, but there was no significant difference between the untreated and plasma-treated fabric since it took the advantage of relatively low temperature. As the plasma treatment increased, however, the lightness of silk fabrics decreased with concomitant increases in the colour intensities of green and yellow [159].
14.3.4 Plasma immobilization Gaseous plasma could be used to add new chemical groups to a material surface and these groups could then be used for attaching a variety of molecules. © Woodhead Publishing Limited, 2010
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(a)
(c)
(b)
(d)
14.15 SEM micrographs of morphology of P. aeruginosa in silk fabrics before (a) and (b) and after (c) and (d) microwave-induced argon plasma treatment for 5 s [158].
The process has a built-in advantage in that it is carried out in a carefully controlled and ultra-clean environment. Low-temperature, low-pressure plasmas can be used for enzyme immobilization on active sites generated by plasma treatment. It is most important to increase the reactivity of the surface of the fibre before enzyme immobilization to enhance the enzyme activity. By using immobilized enzymes the assay procedures could be improved with respect to selectivity, ease of use and analytical sensitivity. In a study, B. mori silk fibroin fabrics were treated with low-temperature plasmas. The effect of using different gases for the plasma treatment on the activity of ALP immobilized onto the silk fibroin fabrics was determined. The gases used were helium, ammonia, nitrogen, oxygen and tetrafluorocarbon. The activities of ALP immobilized on plasma-treated silk fibroin fabrics decreased after plasma treatment with He, NH3 and N2, but when O2 or CF4 gas was used the activities were much improved by the plasma treatments. The plasma
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Ultimate tensile strength (MPa)
100
80
60
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0
0
1 2 3 4 Plasma treatment time (s)
5
14.16 Change of ultimate tensile strength of the fabrics according to the plasma treatment time [158]. Table 14.6 Effect of experimental conditions of the plasma treatment on activity of the immobilized ALP [160] Gas Gas flow rate Power Time (min) (ml/min) (W)
Enzyme activity (unit/g of silk fibroin)
O 2 O 2 O 2 CF4 CF4 CF4 CF4 O2–CF4 O2–CF4
0.169 0.138 0.133 0.129 0.139 0.270 0.170 0.317 0.418
20 20 20 20 20 20 20 20 20
100 200 300 100 200 300 300 300 300
3 3 3 1 1 1 1 1–1 3–1
treatments were performed under various experimental conditions with O2 and CF4 gases. The results are summarized in Table 14.6. The plasma treatments with O2 or CF4 gas were effective in improving enzyme activity under all conditions in this experiment. The highest enzyme activity was obtained by the plasma treatment using CF4 gas after O2 plasma treatment (O2, –CF4, treatment): more than four times that for untreated fibroin. The activity of ALP immobilized on the silk fibroin fibre was much improved by the incorporation of the atomic group –C–O–CF3 into the fibre by CF4 plasma treatment. It was found that plasma treatment of silk fibroin fibres with CF4 gas is very useful for enzyme immobilization [159].
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14.3.5 Bone cement Self-curing acrylic bone cement has been used routinely for over three decades for fixation of metallic prostheses in partial and total joint surgery. In recent years, efforts have been made to improve the performance of existing surgical cements. In one such study the mechanical properties of acrylic bone cement were improved using the plasma modification technique. Yang et al. [160] treated ultra-high molecular weight polyethylene (UHMWPE) fibres with argon plasma for 5 min, followed by uv irradiation in methyl methacrylate (MMA)–chloroform solution for 5 h to obtain MMA-g-UHMWPE grafted fibre. The grafting content was estimated by the titration of esterification method. To improve the mechanical properties of acrylic bone cement, pure UHMWPE fibre and MMA-g-UHMWPE fibre were added to surgical Simplext-P radiopaque bone cement. By comparing the effect of the pure UHMWPE fibre and MMA-g-UHMWPE grafted fibre on the mechanical properties of acrylic bone cement, it was found that the acrylic bone cement with MMA-g-UHMWPE grafted fibre had a more significant reinforcing effect than that with untreated UHMWPE fibre (Fig. 14.17). This might be due to the improvement of the interfacial bonding between the grafted fibres and the acrylic bone cement matrix.
14.3.6 Sutures With the increasing demands for a biomaterial with better acceptability and functionality to the biosystem, stress has been focused on the development of newer materials. One of the ways to develop such materials is to modify existing polymers and design them keeping in view their specific application areas. Sutures are used in surgical operations and require optimum physicochemical characteristics. However, medical reports show that local infections following surgery are very frequent. In these situations, surgical sutures with antibacterial properties provide a promising solution. Biocidal materials and antibacterial finishing of textiles have been reviewed by many authors [161–165]. In general, antimicrobial properties can be obtained by coating or padding the ready-made fibres with bacteriocidal agents or by the addition of antimicrobial agent during extrusion of a polymer [166–176]. Polypropylene (PP) is one of the widely used biostable sutures due to its optimum tensile strength and low level of tissue reaction as compared to other sutures. However, microbial infection on the suture site has often been observed, leading to the deterioration of the wound and related complications, especially where post-surgical care is not well taken up. Therefore, the modification of polypropylene sutures may be carried out in such a way that it acquires functional groups where a drug may be immobilized. This drug is released from the suture once in contact with the biosystem and
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provides antimicrobial action. In our previous work, we carried out the grafting of hydroxyethylmethacrylate onto PP monofilament to immobilize b-hydroxyquinoline as the antimicrobial drug [171,172]. However, the grafting led to considerable homopolymer formation that remained occluded within the polymer matrix and its complete separation from the suture matrix could not be achieved due to the hydrogel nature of the polyHEMA. Thereby, the suture characteristics were greatly deteriorated. Moreover, the inherent incompatibility of the grafted ionic component with the non-ionic PP matrix added loss in tensile strength. In order to overcome this problem, we have carried out the grafting of nonionic monomer acrylonitrile onto the PP monofilament using preirradiation where homopolymerization is very slight and its separation from the grafted PP matrix would be much easier as compared to hydrogel polyHEMA. Moreover, polyacrylonitrile grafts because of their non-ionic nature would provide better compatibility of polyacrylonitrile grafts with the PP base matrix. This may lead to better retention of tensile properties. The grafted PP monofilament was subsequently hydrolysed to get carboxyl groups for subsequent antimicrobial drug immobilization. In our recent study, the grafting of acrylic acid onto polypropylene monofilament by vacuum plasma has been carried out to introduce carboxyl groups on the surface for subsequent antimicrobial drug immobilization and chitosan immobilization [173]. The idea of immobilization of chitosan is to make it scar preventive as well. The variation of the degree of grafting with the reaction time for various plasma treatment times is presented in Fig. 14.18. The graft variation shows identical behaviour for exposure times in the range of 60–240 s. The degree of grafting increases linearly with the increase in the reaction time up to 6 h 3
60
40
2
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1
Tensile modulus (GPa)
Tensile strength (MPa)
Tensile strength Untreated fibre Modified fibre
Tensile modulus Untreated fibre Modified fibre
0
0
2 4 Uhmwpe content (wt%)
6
0
14.17 Effect of fibre content on tensile properties [162].
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Degree of grafting (mg/cm2)
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180 s 240 120 s 160 60 s 80
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2
4 6 Reaction time (h)
8
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14.18 Variation of the degree of grafting with reaction time for different plasma treatment times. Plasma treatment conditions: plasma power, 100 W; O2 pressure, 20 sccm [175].
Degree of grafting (mg/cm2)
50
40 30
Gel formation
20
10 0
20 40 60 80 Monomer concentration (%)
100
14.19 Variation of the degree of grafting with monomer concentration. Plasma treatment conditions: exposure time, 60 s; plasma power, 60 W; O2 pressure, 20 sccm. Grafting conditions: water–methanol, 60:40; temperature, 50∞C; time, 2.5 h [175].
and then levels off. It may be stated that the growing chains are exhausted within 6 h and lead to the equilibrium degree of grafting. The grafting yield increases with the increase in the plasma treatment time due to the enhanced number of active species involved in the grafting reaction at longer plasma treatment times. The variation of the degree of grafting with the monomer concentration is presented in Fig. 14.19. The grafting increases with the
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increase in the monomer concentration up to 40% and subsequently tends to decrease. The initial increase in the degree of grafting with the increase in the monomer concentration is probably due to the unhindered accessibility of the monomer to the primary radicals P·, resulting in a smooth initiation step and the propagation step. No homopolymerization takes place at 10% monomer concentration (Table 14.7). The homopolymerization is still very slight (4%) for 20% monomer concentration. At 30–40% monomer concentrations, a large fraction of the monomer is transformed into the homopolymer, but still leaves behind some monomer for the grafting process to follow. With subsequent increase in the monomer concentration (>40%), the homopolymerization is extensive and the viscosity of the reaction medium increases significantly, which causes the monomer depletion as well as diminishing monomer accessibility to the grafting sites. The homopolymerization is so intense beyond 60% monomer concentration that the grafting does not takes place at all. The contact angle of filaments shows interesting behaviour depending on the grafting with acrylic acid under specific conditions. The exposure of the filament to the oxygen plasma leads to a significant reduction in the contact angle from 88° for the original filament to 32° for the exposed sample for a treatment time of 60 s, as represented by the open circle on the y-axis in Fig. 14.20. This is the indication of the surface functionalization of PP by plasma treatment which involves various groups such as carbonyl, hydroxyl and hydroperoxides. However, this history of functional groups on the surface changes as the polyacrylic acid chains are incorporated. The contact angle of the samples with different graft levels and prepared under different reaction media is presented in Fig. 14.20. The contact angle decreases with the increase in the degree of grafting. The results show that the transition to a minimum contact angle takes place beyond ~20 mg/cm2 graft level and a minimum contact angle of 23° was achieved for a graft level of 42 mg/cm2. As compared to ferrous sulfate and butanone, both the acetone and methanol produce high graft levels and show identical contact angle values. A precise evaluation of the contact angle of samples grafted in ferrous sulfate and butanone (having close graft levels) shows very Table 14.7 Homopolymer yield at different monomer concentrations [174] Monomer concentration(%) Homopolymer yield (%) 10 20 30 40 50 60
0 4 36 55 72 gel
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Acetone Methanol Butanone FeSO4
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40 Plasma exposed PP filament 20
0
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20 30 40 Degree of grafting (mg/cm2)
50
14.20 Variation of the contact angle with the degree of grafting under different additives [75].
interesting observations. Ferrous sulfate produces surfaces which have a higher contact angle than that produced by the butanone. For instance, the contact angle is 72° and 60° for a graft level of ~8 mg/cm2 for ferrous sulfate and butanone addition, respectively. Probably, the inhibitory action of ferrous sulfate is so pronounced that it deactivates primary radicals or the radicals produced by hydroperoxide decomposition even before the grafting process is initiated. Moreover, whatever grafting is initiated from the remaining sites, the propagating chains are also deactivated fast, leaving behind short chains. This reflects the fact that the ferrous sulfate addition introduces lower hydrophilicity as compared to the butanone addition. The influence of organic additives is so mild that it allows chains to propagate before terminating them and this leaves behind a more hydrophilic surface. Keeping these observations, a tentative mechanism of surface management under ferrous sulfate and butanone is proposed in Fig. 14.21 [73].
14.3.7 Tissue engineering Millions of surgical procedures are performed annually to treat patients suffering from organ disorders. An organ from a donor is still regarded as the best and most reliable alternative for organ transplantation from donor to needed patients. This approach faces the shortage of viable and compatible human donors required for organ transplantation. Another alternative to transplantation is autologous graft, but the availability of viable donor tissue for surgical reconstruction is not always possible. The problems faced by organ and autologous transplantation can be solved by growing specific cells
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FeSO4 PR Pronounced PR/GR deactivation Plasma
Grafting Organic solvents
PP filament
Surface functionalized filament PR stands for primary radicals GR stands for growing chains
Moderate PR/GR deactivation
Grafted filament
14.21 Schematic representation of the grafting process under different reaction conditions [75].
on scaffolds prepared from extracellular protein matrix (ECM) or synthetic polymers. With the increasing demand for polymers in tissue engineering in treating patients for the loss or failure of an organ or tissue, it is becoming necessary to design and develop a polymer for immobilization of biologically active molecules and living cells [174–179]. The polymers are made into scaffolds of the required shape and size, and living cells from the patients are seeded onto the polymer surface and are harvested as tissue for its subsequent transplantation to the patient. The expanded tissue is therefore structurally integrated in the body. This overcomes the problem of donor shortage and transplant rejection of the biomaterial [180]. The innovation in this area is that it opens up a straightforward route to the harvesting of many of the body parts without biological complications. Tissue engineering presents enormous challenges and opportunities for material scientists from the perceptive of both the material design and material processing. The polymers have either no functional groups or a very low level of functionality if at all, which may not necessarily lead to a boil-interactive surface. Such polymers, therefore, need selective modification of their surfaces to introduce functionality, such as hydroxyl, carboxyl, amino and imino groups in a sufficiently large quantity. These functional groups act as sites for the immobilization of proteins and subsequent seeding of human cells. The modification of polymers may be achieved by the graft polymerization of specific monomers by ultraviolet, plasma and high energy radiation. The first two methods are surface selective and hence the graft modification remains confined to the depth of a few nanometres of the surface of the polymer. Plasma-induced graft modification has proven highly successful as a means to develop functional interfaces for the immobilization of biomolecules and cell cultures [105].
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The combination of plasma techniques with wet chemistry treatment leads to biomaterials that optimize cell growth. For instance, to enhance corneal epithelial cell attachment and growth, an ammonia plasma treatment has been applied to artificial corneas fabricated from poly(hydroxyethyl methacrylate) [180]. Figure 14.22 shows the growth of stem cells onto knitted polyester fabric before and after oxygen plasma treatment. Before the plasma treatment, only a few cells attach and are cultured on the textile. The increase in cell growth can be linked to an increase in wettability and the introduction of oxygen-containing functional groups. The attachment of cells is the first step for cell culturing on substrates. The contact of synthetic materials with biological fluids leads instantly to an unspecific adsorption of proteins onto the material surface. In most applications, this is undesirable because bacterial cells will also adhere to the material surface due to proteins in their extracellular matrix. Bacterial adhesion is often referred to as ‘biofouling’. Plaque on teeth or blocking of catheters can result from this effect. Polyethylene glycol (PEG) is an amphoteric material that decreases the adsorption of proteins and the adhesion of cells. PEG is used as the benchmark for comparing new antifouling materials [181,182]. PEGylated surfaces are of interest in biomedical applications. The simplest surface modification technique, direct adsorption of PEG, leads to only weak bonding behaviour. Gombotz et al. [183] used allylamine plasma glow discharge to introduce amine groups onto the surface of poly(ethylene terephthalate), which were subsequently reacted with amine-terminated PEO using cyanuric chloride chemistry. A significant reduction in the adsorption of albumin and fibrinogen was achieved, despite an incomplete surface coverage. Ratner and coworkers [184,185] have demonstrated that PEG-like surfaces, which resist protein adsorption and cell adhesion, can be formed using plasma deposition of short-chained oligomers. Figure 14.23 shows the results of minimizing unspecific protein adsorption (IgG) using different surface modifications. The measurements 100 mm
100 mm
14.22 SEM pictures of stem cells attached onto a polyester fabric after plasma [182].
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Plasma grafting after O2-activation
150
Plasma grafting after N2-activation
487
Plasma fixation using Ar
120 90 60 30 0
Hema (peo-ppo-peo)90 Vinyl(Allyl-PEO)1100 imidazole (Allyl-PEO)250 (peo-ppo-peo)250 VinylEthoxide pyrrolidone Type of surface modification
Unmodifed
14.23 Minimization of unspecific protein adsorption (IgG) through different surface modifications [188].
were carried out after a stability test using 1 m NaOH for 1 h at 50°C, and different plasma-based techniques were investigated. Grafting after activation with oxygen or nitrogen plasmas and plasma fixation experiments were carried out. The best results were obtained with (PEO–PPO–PEO)250 fixed after a dip coating and with a consecutive plasma treatment. Polypeptide growth factors are powerful regulators of a variety of cellular behaviours, including cell proliferation, migration, differentiation and protein expression, and these molecules are being developed as important therapeutics in tissue regeneration, e.g. in closing bone defects and in healing chronic ulcers in the skin. The ability of immobilized growth factors to remain biologically active has been demonstrated in the very well-characterized system of epidermal growth factor conjugated to synthetic polymer surfaces, where it was shown to be capable of directing hepatocytes to maintain their liver-specific morphology and function [186].
14.4
Conclusions
Biomaterials, which have permanent contact with the body and tissues, require unique surface properties such as surface free energy, hydrophilicity and specific surface morphology, for improved cell/protein adhesion on the polymer surface. Textile materials offer porosity and compliance which are often not exerted by other polymeric materials. Textile materials and products that have been engineered to meet particular needs are suitable for any medical and surgical application where a combination of strength, flexibility and sometimes moisture and air permeability are very much required. Different forms of textile materials are used, including monofilament and
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multifilament yarns, woven, knitted and non-woven fabrics and composite structures. Surgical implantation of these materials is encountered with both thrombosis and inflammation at the site of injury. These processes are related, and both contribute to the healing of tissue into and around the material. Ability to modify a surface in a controlled way, deposition of crosslinked films on complex geometries, formation of multilayer films, rapidity, sterility and the prospect of scalingup are the salient features of plasma processing that makes it suitable for biomedical applications. The main requirement of the material is bioreceptivity and biocompatibility along with functional performance at the application site in human beings. For this requirement, it is necessary to modify the materials before use in biomedical engineering. Plasma technology is widely used to alter the surface properties of polymers without affecting their bulk properties. The objectives of plasma surface modification in biomedical applications are adhesion promotion, enhanced surface wettability and spreading, and reduced surface friction. Applications of plasma-based systems used to process materials are diverse because of the broad range of plasma conditions, geometries and excitation methods that may be used. The scientific underpinnings of plasma applications are multidisciplinary and include elements of electrodynamics, atomic science, surface science and industrial process control.
14.5
References
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183. Gombotz W R, Wang G H, Horbett T A, Hoffman A S, J Biomed Mater Res, 1999, 25(12), 1547. 184. Ratner B D, Mar M N, Yee S S, Sensors and Actuators, 1999, B 54, 125. 185. Ratner B D, Shen M, Wagner M S, Castner D G, Horbett T A, Langmuir, 2003, 19(5), 1692. 186. Kuhl P R, Griffith-Cima L G, Nat Med, 1996, 2, 1022.
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Technical sewing threads
R. S. R e n g a s a m y and S. G h o s h, Indian Institute of Technology, Delhi, India
Abstract: The first part of this chapter deals with ‘industrial threads’ in general and the second part is dedicated to a specialized application on ‘surgical threads’. The structure of industrial threads and their finishing, threads used for high temperature, outdoor and airbag applications are discussed. Properties of ceramic, silica, glass, steel-core, aramid and PTFE threads are discussed. Surgical sutures are classified. Forms, manufacturing processes, and physical, handling and biological characteristics of sutures are described. Key words: automotive, sun protection, filtration, core-spun, monocord, air-entangled, absorbable sutures, non-absorbable sutures, knot security, biocompatibility.
15.1
Introduction
A wide variety of sewing threads is available on the market catering to nonapparel end-uses. These ‘technical threads’ can be divided into ‘industrial threads’ (used to stitch or join materials or fabrics) and ‘surgical sutures’ (used for medical applications in wound closure), the two types of threads falling into altogether different domains and having quite different requirements. Technical sewing threads are developed specifically for each application and need specific properties to meet individual requirements; as a rule, their use is clearly defined by the item to be produced. Fashionable and creative aspects are not of primary concern. The first part of this chapter deals with industrial technical sewing threads in general whilst the second part is dedicated to the specialized application of ‘surgical threads’.
15.2
Industrial sewing threads
Numerous non-apparel industrial sewing threads are available on the market catering for various applications. These sewing threads can be divided into those used in the following categories [1]: ∑ ∑
Automotive and supply industries: airbags, safety belts, convertible car covers, interior fittings, seats/upholstery, steering wheels, etc. Sun protection: awnings, winter garden shades, venetian blinds, shade installations, etc. 495 © Woodhead Publishing Limited, 2010
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Multi-needle stitching: mattresses, bed quilts, sleeping bags, tents, tarpaulins Protection: heat-resistant clothing, work shoes, work gloves, cleanroom clothing, bulletproof vests, lumberjack trousers, container sacks, parachutes, etc. Geotextiles: to stitch woven/nonwoven fibrous materials used for covering disposable wastes and natural or artificial embankments Filtration: to stitch filter fabrics used for filtering gases and liquids Leather goods: shoes, bags, etc. Other applications: for example, tea bags, book binding, phosphorescent threads, etc.
Threads for non-medical applications are machine- or manually-sewable. Technical threads are mostly heavy as the fabrics to be sewn are themselves generally very thick and heavy. Many heavy-duty industrial sewing machines are available on the market to sew industrial fabrics, from manufacturers such as Adler, Brother, Juki, Kansai, Mitsubishi, Pfaff, Rimoldi and Singer. Sewing by machine is a complex process, yet the process has been so perfected by the machine manufacturers that it is carried out at extremely high speeds on modern sewing machines; despite this, sewing technology is still being developed to increase those speeds. Trouble-free sewing, or sewability, has to be the first requirement for making textile or non-textile products. Defective stitches, fabric yarn destruction, chaffing and melting of sewing threads, missed stitches and puckering are primary concerns when joining two or more pieces of material together during machine sewing [2]. Sewing thread manufacturers can influence sewability by varying the thread extensibility, thread friction (between thread and fabric, and thread and machine parts) and twist balance between single and ply twists [3]. Sewing threads should possess the required loop and knot strength to meet the intended applications and sewing conditions (sewing speed, type, construction and number of plies to be sewn). They should be highly uniform (with no knots, thick or thin sections, or neps) to pass through the needle eye without breaking. They need good abrasion resistance for easy sewing and for the long life of the sewn product. The surface of sewing threads is sized with lubricants to reduce friction during sewing. Further, synthetic filament threads must be coated with coolants to reduce frictional heating of the needle so as to avoid melting and breaking of threads during sewing. In high speed sewing, an additional lubricating unit must be fitted on the sewing machine to reduce excessive needle heating.
15.2.1 Structure of industrial thread Sewing threads can be classified into spun, core-spun, twisted multifilament, draw-textured, monocord, air-entangled, air-textured, monofilament and tape, © Woodhead Publishing Limited, 2010
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based on their structure, construction, methods of manufacture and form of constituent fibres. Photographs of some of the sewing threads appear in Fig. 15.1. Spun thread Two or more spun yarns are plied to make a thread of the required thickness. During the plying operation, twist is applied in the opposite direction to that present in the single yarns to avoid snarling during sewing. Further, the twist is set in by heating through an autoclave. Spun threads have fuzzy surfaces giving them a soft feel, bulk and good lubricity. Spun threads are made from cotton, polyester, Nomex and Kevlar, polyester–cotton blends, viscose, wool and acrylic fibres. Core-spun thread Staple fibres are wrapped around a core of continuous filament yarn on a ring spinning machine and then single yarns are plied. They are similar to spun threads in terms of hand and lubricity but are more uniform in diameter than spun threads. In addition, the core consists of very strong multifilaments, imparting high strength and durability to the thread and hence allowing the use of smaller thread sizes for the same seam strength than spun threads. Polyester core-spun threads are the most widely used threads in a variety of sewing applications. To improve resistance against needle heat during sewing on machines, cotton fibres can be wrapped over polyester filament yarn (i.e. in polyester–cotton core-spun threads). For excellent thread chemical
(a)
(b)
(c)
(d)
(e)
(f)
15.1 Sewing threads: (a) Nomex filament; (b) nylon filament bonded; (c) polyester–polyester core-spun; (d) polyester–cotton core-spun; (e) polyester spun; (f) polyester texturized.
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resistance and colour fastness, polyester staple fibres are used on the sheath. Threads are also made with polyester in the core and rayon on the sheath, and with polyurethane in the core and nylon on the sheath. Twisted multifilament thread Continuous filaments are twisted together into a cohesive bundle and then plied to form a thread, dyed, stretched, and heat set to achieve the desired physical characteristics. They are made as soft threads or given an additional bond for better ply security and abrasion resistance. They are strong for their size and durable. These threads give high friction during sewing and generate sufficient heat in the needle to soften the thermoplastic fibres and cause fusing [4]. Twisted multifilament threads are made from fibres such as polyester and nylon (both high tenacity), Kevlar®, Nomex®, coated E-glass, coated polytetrafluoroethylene (PTFE), poly ether ether ketone (PEEK), Spectra®, metallized threads (from nylon, polyester or rayon), polypropylene and acrylics. Draw-textured thread Multifilament yarns are draw textured and then heat set to improve bulk retention. Regular, medium tenacity polyester yarns are usually used and are less expensive compared to other threads. To a limited extent, polypropylene filaments are also textured for thread making. Draw-textured threads, by virtue of their crimp rigidity, are very soft and extensible. They are used for covering very extensible seams in knitwear, underwear, swimwear, foundation wear and tights, since they are very soft on the skin [5]. Draw-textured threads are not suitable for industrial applications due to their high extensibility. Monocord thread Continuous filaments with little twist are bonded together by resins and then lubricated to form monocord threads. Their appearance is flat and ribbon-like and hence they possess very high abrasion resistance and provide excellent seam durability. They are very strong for their size and find use in heavyduty industrial applications such as sewing of furniture, leather and sporting goods, luggage and shoes. UV inhibitors are often incorporated into the resin during the resin bonding process [6]. In view of the comparative ease of bonding nylon compared with polyester, nylon is predominantly used for bonded continuous filament threads. Most threads are hot-stretched to give them high modulus and breaking extension.
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Air-entangled threads Air-entangled threads are composed of a continuous polyester filament core surrounded by filaments that have been entangled by an air-jet. The core contributes strength and the entangled surface filaments increase fullness and reduce friction [5]. After entangling, they are twisted, dyed and applied with lubricant. They have high initial modulus and hence have an excellent loop forming characteristic. They are not as soft as spun polyester threads and are less expensive than core-spun and spun threads. With excellent seam durability and security, they are used for all types of stitches (lockstitch, chain stitch, over edge, etc.) in garments and furnishing applications. Air-jet textured threads Continuous polyester filaments are bulked and entangled using a supersonic air-jet. The resultant yarn has many surface loops which provide a less slippery feel and better seam security than continuous filament threads. Mostly medium tenacity filaments are used [5]. Threads are not produced by a traditional process, being processed instead directly from yarn to a dyeing package [1]. They are sometimes used for heavy applications, such as for furniture and jeans, but often in less demanding applications [7]. These threads have a soft handle and are primarily used where a soft seam is required. Twisted or plied sewing threads are stronger and have less friction than those threads which are only textured and lubricated. Air-jet textured threads are far more uniform than spun threads [8]. Air-textured polyester threads made without silicon finishes are used for sewing container bags. Monofilament threads Monofilament threads are produced mainly from nylon monofilament, and to some extent from polyester. They are translucent and blend with many colours. Because of their stiffness they are not preferred for seaming clothes to be worn adjacent to the skin. Seam security sewn from these threads is poor as they are stiff and unravel easily if a thread breaks or is not locked adequately in the seam [2]. Tape threads Tape threads are made from tapes, including from fibrillated tapes. ePTFE fibres are available in tape form, and Amann manufactures threads based on Tenara, in both tape and twisted tape forms. Polypropylene threads are also available as fibrillated tapes.
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15.2.2 Thread finishing Threads are finished in different ways to enhance their machine sewability and suitability for various end uses. Various finishing processes are available: ∑ ∑ ∑ ∑
∑ ∑
∑
Soft finish: Thread does not receive any finish except dyeing and lubrication. Mercerizing: Cotton spun threads are subjected to a caustic solution treatment under controlled tension to improve lustre and strength. Gassing: 100% cotton and cotton-wrapped polyester threads are singed to reduce fuzz and to improve sheen prior to mercerizing and dyeing. Glazing: 100% cotton and cotton-wrapped polyester threads are treated with starches, waxes and special chemicals, and then polished/brushed for high lustre. The finish protects the thread from abrasion and enhances ply security during sewing of hard fabrics. Bonding: multifilament polyester or nylon is treated with special resin that binds the filaments, forming a tough, smooth protective coating to the thread, thus improving ply security and abrasion resistance. Lubrication and other treatments: Threads are lubricated to reduce friction. Wax, silicone, silicone-wax, etc., is used. Silicone-finished thread has better needle-cooling properties and provides more uniform thread delivery for consistent stitch formation. However, for those applications where the prevention of lube transfer is a major concern, or for uses which are mandated to be silicone-free (children’s sleepwear, for example), wax is used. In many applications, synthetic threads are now finished with a variety of resins and chemicals along with lubricants to meet the end use requirements; these finishes include acrylic (water repellency), PTFE (UV protection and anti-wicking for marine and outdoor applications), thermal and chemical resistance (for filters), Halar (for thermal and chemical corrosion resistance), a semi-conductive finish for safety wear, a nonwick finish to prevent capillary action of water through a sewn seam for military applications, a heat-resistant finish to protect the thread from needle heat, and many others. Each thread manufacturer develops their own thread sizing/finishing formulation, the detail of which is kept as a closely guarded secret, and hence not available in the public domain. Polyurethane finishes are applied to nylon and polyester threads meant for awnings and boat covers to improve resistance to UV, abrasion and low temperature flex.
15.2.3 Thread numbering and packaging Over the years, the labelling of threads by manufacturers using ticket numbers has become confusing rather than informative. The American Textile Manufacturers’ Institute (ATMI) proposed the ‘Tex system of numbering’
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for industrial sewing threads. The same system has been incorporated into standard practice by ASTM (ASTM D 3823). According to this standard, the ticket number of a thread is defined as the tex of the thread before wet processing and finishing. Threads are packaged into different forms/contents/ shapes catering to different markets and types of sewing machines. The common thread packages available on the market are shown in Fig. 15.2.
15.2.4 Sizes of threads and fabrics The thickness, size and linear density of a sewing thread (in tex) must be selected based on the weight of the fabric to be stitched, measured in grams per square metre (gsm). Table 15.1 provides guidelines to select sewing threads for various classes of fabrics [9]. Fabric type (construction, fibres, etc.) and thread bulkiness also have to be considered in selecting the right thread–needle combination.
15.2.5 General properties of fibres used for sewing threads The physical, mechanical and functional properties of various fibres used to make different sewing threads are given below: ∑
Cotton: low strength and elongation, less durable, colour fastness
(a)
(b)
(c)
(d)
15.2 Thread packages: (a) bobbin; (b) kingspool; (c) cap; (d) cone. Table 15.1 Thread selection chart Fabric size, gsm
Thread size, tex
Metric needle size
65–140 140–205 205–275 275–340 340–480 >480
16–24 24–30 30–50 40–60 60–105 120–300
65–70 75–80 80–90 90–110 110–125 130–230
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∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑ ∑
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not as good as polyester, good heat resistance, poor rot and mildew resistance Viscose: medium strength, low elongation, low wet-modulus and high sheen Polyester: high strength, high elongation, very good colour fastness, very good abrasion resistance, good dry and wet strength retention, very good UV resistance, and poor alkali resistance Nylon: high strength and elongation, excellent abrasion resistance and elastic recovery, and good chemical resistance Para aramid: very high strength and cut resistance, low elongation and excellent short term heat resistance Meta aramid: inherently flame retardant, very high strength and elongation and excellent long-term heat resistance High modulus polyethylene: extremely high strength and excellent chemical resistance Polypropylene: highly hydrophobic and resistant to salt water PTFE: chemically inert with excellent resistance against sunlight and extreme weather Glass: chemically inert, brittle and resistant to high temperature Ceramic: resistant to extreme high temperature and low thermal expansion Steel: excellent antistatic properties and very high strength.
15.2.6 Threads for automated multi-directional sewing These threads are manufactured by an air-entangling process. They have a high degree of uniformity of continuous filaments, excellent loop-forming characteristics and seam security. When constructed without twist they have a high multi-directional sewing performance and can be used in sewing with automated stitching jigs. A few commercial air-entangled polyester threads have been developed for high-speed automated sewing (multi-directional sewing) applications for lightweight lingerie and upholstered furniture. These threads have excellent loop strength, and the tensile breaking strength of a single end may be around 5–6 gf/denier. The technical applications of these threads are for fleece goods, flags (27, 40 tex), upholstery and mops (60, 90, 135 tex). The threads are made with elongation at break and dry shrinkage values set at 18% and 2–2.5%, respectively, [10].
15.2.7 Threads for very high temperature applications Threads for very high temperature applications are required to hold the seam and secure it in extreme temperatures between 500 and 1100˚C. They are made from ceramic, glass, quartz and carbon fibres. Threads made from
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carbon and quartz are very expensive and are produced exclusively for military and aerospace applications. Ceramic-fibre thread consists of several strands of continuous ceramic fibres (graphite, silicon carbide or refractory metal oxide) and is covered with organic-fibre yarn [5]. Ceramic threads 3M has developed threads with ceramic and rayon fibres, namely Nextel 312 and 440, the rayon constituting 5% by weight on the surface [11]. The rayon on the sheath gives resilience to the thread to improve its sewability and decomposes at 300˚C. The ceramic fibres, made from aluminium oxide, have very high breaking load and modulus. The addition of SiO2 and B2O2 to aluminum oxide reduces the stiffness and thermal expansion of the fibre to a greater extent than it does the tensile strength. Table 15.2 compares the properties of ceramic fibres with various compositions. These threads are suitable for sewing ceramic-fibre fabrics such as tapes, sleeks and other high temperature fabrics. Custom blankets, seals, gaskets, curtains, zone dividers, shaped quilted items, and fabrication of high temperature sewn parts are made from these threads. The threads are pre-coated with an organic lubricant or unsized. Any coating has to be removed at 700˚C in controlled conditions if the fabrics are to be used for composites, electrical insulation of thermocouples and heater applications. The sized threads have higher strength than the heat-cleaned ones. Unlike
Table 15.2 Properties of ceramic fibres of different chemical compositions
Nextel 312 Nextel 440
Nextel 550 Nextel 720 Nextel 610
Chemical composition, %
62.5 Al2O3 24.5 SiO2 13 B2O2
70 Al2O3 28 SiO2 2 B 2O 2
73 Al2O3 27 SiO2
85 Al2O3 15 SiO2
>99 Al2O3
Melting point, ˚C
1800
1800
1800
1800
2000
Filament diameter, μm
10–12
10–12
10–12
10–12
10–12
Density, g/cm3
2.7
3.05
3.03
3.4
3.9
Tensile strength, MPa
1700
2000
2000
2100
3100
Tensile modulus, GPa
150
190
193
260
380
5.3
5.3
6.0
8.0
Thermal expansion 3 at 100–1100°C, ppm/°C Source: 3M.
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regular fibre-threads, ceramic fibres are brittle and thus the knot strength of ceramic threads is very much lower compared to their tensile strength (about 20% of tensile strength). They are suitable for sewing on heavy duty 301 lock-stitch machines with a speed of 550 stitches per minute, and are available in 0.48–0.74 mm diameters (styles AT-21 and BT-30) and about 316 to 700 tex. These threads are non-oxidizing and non-hygroscopic, and have very high thermal resistance (1100–1300°C) and high melting point (1800°C). NextelTM threads 312 and 440 are machine-sewable, used for fabricating high temperature sewn parts. They are pre-coated with an organic lubricant and need no soaking or further lubrication on the machine. It is recommended not to use lubricants such as silicone, PTFE or soap as they damage the high temperature properties of the thread. The coating on Nextel sewing threads 312 and 440 may decompose to hazardous by-products if the sewn products are heated. Heat processing to remove coatings must be done with exhaust ventilation which provides minimum capture velocity of 46 m/min. It is recommended to refer to the heat cleaning instructions and health and safety bulletin issued by 3M. A Style BT-30A thread (about 0.74 mm diameter and 700 tex) requires a needle size 26 on a 301 lock-stitch machine for smooth passage of the thread. The recommended tension settings for needle and bobbin threads are 600 and 400 cN, respectively, for stitching of two layers of fabrics, so that the interlocking of threads takes place on the bottom side of the fabric surface. For sewing multiple layer parts, a buried stitch may be desired. 1.5 to 2.8 stitches per cm is recommended; a higher stitch density can damage fabrics and leads to excessive thread breaks. Foot pressure has to be optimized considering the occurrences of thread slipping and crushing at low and high pressures, respectively. Silica fibre threads Silicon carbide threads have high breaking strength retention after exposure to temperatures above 1000°C. These threads are usually sized with PTFE or wrapped with viscose or polyester yarn and used for the stitching of blankets for the thermal protection system of a space shuttle. Astroquartz®, fibres are made from high purity, extremely fine continuous filaments of pure fused silica (99.99% SiO2). These fibres are capable of withstanding extended exposure to 1100°C and have near-zero coefficients of thermal expansion, high temperature performance and the excellent mechanical properties required for composites in aerospace applications [12]. Astroquartz® II sewing thread is made from such fibres and is mostly supplied coated with Teflon (20%). Because of its high strength and flexibility, and high purity and high temperature resistance, Astroquartz® II sewing thread
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is widely used in sewing or wrapping insulation blankets, shrouds, blast curtains and separators. The diameters of threads vary from 0.36 to 0.61 mm with breaking strengths of 67–90 N. Basalt fibres are produced from certain types of rocks and minerals by high temperature melting and refrigeration. Various chemical compositions or minerals of basalt influence the properties of their melts and consequently their suitability for forming fibres. The chemical compositions of rocks suitable for basalt fibre production are given in Table 15.3 [13]. Basalt fibre has the characteristics of both asbestos and fibreglass, but also has other kinds of excellent capabilities. Some of the characteristics of basalt fibres are: ∑ Temperature resistance from –270∞ to 700∞C (holding temperature) ∑ Very high elastic modulus ∑ High corrosion resistance to acid and alkali ∑ Smooth surface like silk and a soft feel. Basalt threads are twisted and widely used in sewing of high temperature resistant fabrics and filter bags. A thread of 208 tex has about 6 mm diameter with a twist of 280/m. Glass threads Fibreglass sewing threads made from E-glass yarns consist of very fine fibres which are plied and twisted. These threads have a smooth surface and high strength, and are resistant to high temperature and corrosion. Threads made from glass fibre are best suited to high temperature filtration (filter bags) and welding applications due to their resistance to acids, organic solvents and other chemicals, and their stability at high temperatures [14]. Threads made from E-glass continuous filaments are less expensive. To improve the sewability, glass is coated with PTFE (12–18% w/w). A uniform and continuous coating is essential to enhance the flexibility of the fibreglass yarn, minimizing the tendency to kink, strip-back or break and increasing the resistance to a build-up of contaminants and repelling attack by most acids and alkalis. W.F. Lake Corporation manufactures PTFE-coated E-glass sewing threads (TEF) which retain 50% of their original strength at 350∞C, withstand 290∞C and 550∞C (continuous and intermittent operations, respectively) and are UV resistant. They are suited for safety spray shields, high temperature gaskets/textiles, insulation jackets or pads, kiln seals, welding blankets and Table 15.3 Chemical composition of rocks suitable for producing basalt fibres Compound SiO2 % Range
Al2O3
45–60 12–19
Fe2O3 CaO
MgO
TiO2
Na2O, K2O
Others
5–15
3–7
1–2
2.5–6
2–3.5
6–12
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heat shields. Beta-glass threads are made of finer filaments and are suitable for applications requiring continuous flexing and bending of threads. 3M has developed PTFE-coated glass filament threads GT-15 and GT-23, with 240 and 395 tex, respectively [11]. The breaking strength after heat cleaning drops by 50%. These threads are recommended for use up to 760°C of continuous operating temperature, and are found in applications such as seat blocking for aircraft and high temperature garments (suits, gloves), etc. They do not corrode and are temperature resistant up to 540°C, decomposing at 815°C. For the manufacture of decorative fabrics, cable braiding and similar applications, dyed threads with limited colours are available. Steel-core threads Steel-core threads consist of 80% steel covered with Nomex, Kevlar, FR cotton, FR viscose or flame resistant synthetic fibre [15]. To facilitate easier machine sewing, steel core is covered with cotton fibres and lubricated. These threads are used in military and safety applications in view of their excellent heat resistance. They are also used to dissipate static electricity in applications such as flooring for computer rooms and in places where electricity can severely damage expensive machinery [5]. Other antistatic applications include stitching of workwear, coats, gloves, suits, etc. Typical threads are three-plied with linear density ranging from 235 to 470 denier, having tenacity around 150 cN/tex. 100% stainless steel threads are used for very high temperature and flame resistance applications up to 800°C.
15.2.8 Aramid threads Aramid threads are made from aramid fibres such as Kevlar, Nomex and Technora. Their unusual characteristics have enabled the development of many new products that were not feasible before. Kevlar is, by weight, five times stronger than steel. Nomex has superior heat resistant characteristics. They are used in many applications, including ballistic clothing, fire suits, wire and cable applications, etc. While these fibres are chemically similar, they are different in other ways. Threads made of Nomex are flame retardant and do not char at temperatures higher than 360°C, making Nomex extremely desirable in safety garments used in potentially high temperature applications (e.g. race suits and thermal protection clothing) or in the filtration of hot gases (where they are widely used) [16,17]. Although thread made of Kevlar has slightly less fire retardant properties than Nomex (its LOI is 25–28 compared to that 30 for Nomex), it is preferable in applications requiring extreme strength and heat protection. There is a demand for sewing thread that is highly resistant to fire and heat to sew layers of fire-retardant fabrics together, for uses such as in bedding,
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institutional window treatments, and for protective safety apparel. Impending US Government regulations mandate the use of such threads in products such as bedding. Currently, the predominant product used for these types of applications is made from para-aramid staple fibres, such as Kevlar, with a breaking elongation which is inherently low. Due to this, Kevlar threads typically exhibit less than exemplary sewing performance, and require the thread to be produced from finer yarns and then plying two or three yarns together. The cost of such sewing yarns is also exceptionally high. A composite thread consists of a core of glass filaments that have an elongation of less than 4%. The core is wrapped in a sheath of micro-denier para-aramid fibres that are ring spun with sufficient twist to cause contraction of the core, and then lubricated to lower friction during sewing.
15.2.9 PTFE fibre thread PTFE fibre threads have excellent resistance to solvents, acids and abrasion and hence find applications such as filter bags for hot-gas filtration, protective clothing, marine uses, braiding for new aircraft engines, etc. [18]. Sewn filter media such as filter bags and cartridges are exposed to extreme temperatures, chemicals, abrasives and, occasionally, moist environments for extended periods. These conditions degrade the filter media and thread, and the sewing threads often degrade or wear out first. Appropriate sewing thread has to be used for sewing the filter media and, in the case of pure filtration applications, the thread should not contain finishes to avoid any contamination. Rastex® is a sewing thread that is manufactured from Gore’s 100% expanded PTFE fibres and engineered specifically for the demands of filtration applications, and that withstands exposure to chemicals, high temperatures, abrasives and moist environments [19]. It does not use finishes or coatings and is chemically inert to alkalis, acids, solvents and hydrocarbons, with temperature resistance from –212 to 288°C. It is non-contaminating due to its low surface energy and is non-ageing, with low shrinkage at high temperature and a high limiting oxygen index (95%). The tenacity values of Rastex® are around 25 and 8 cN/tex at ambient temperature and 250∞C, respectively, which is higher than for other PTFE threads. Rastex® threads for filter applications are available in two sizes (regular 133 tex; heavy 267 tex). Most high-temperature threads break and skip stitches during sewing. For optimum sewing results, it is recommended to use light tension and the proper needle size. These threads have better gliding properties as they have low friction compared to fibreglass, polyester and Nomex threads, and are expected to have superior performance during sewing operation. PlastolonTM thread, made from ePTFE fibres, has high tenacity, low shrinkage and excellent chemical resistance characteristics essential to the filtration industry. These threads are available in various deniers (100 to
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2400) with different formats: flat, folded, twisted or staple. The tenacity and elongation of these threads are 27 cN/denier and 5%, respectively. The temperature resistance is –300 to 500°F. Conventional seam threads used to stitch awnings and other outdoor fabric products suffer from exposure to wind and weather, especially to UV light. Conventional threads on outdoor fabrics can become brittle and break after a few years. Threads made from ePTFE have very high resistance to UV light, cleaning agents, salt water and extreme weather (high temperature, acid rain and frost). Tenara® sewing threads made from Gore’s ePTFE fibres are marketed for outdoor application (awnings etc.) and, in fact, are guaranteed to outlast the fabric on which they are used! These threads are pigment dyed, extremely colourfast and ideally suited for use in outdoor and marine fabric applications. Plastomer Technologies make sewing threads based on ePTFE fibres. Solar ThreadTM, which has high strength retention as well as UV stability and a hydrophobic nature, is suitable for outdoor applications such as boat covers, awnings, tents, umbrellas and convertible car tops. W.F. Lake Corporation manufactures twisted fibre thread from 100% pure expanded PTFE fibre, one of the most chemical-resistant threads on the market today. It does not degrade from continuous exposure to the sun, will not rot, and will not support fungus or mildew. In addition, it is unaffected by fuel, cleaning solvents, salt water, motor oil, etc., making the sewn seams as long-lasting as the fabrics or filter media. This thread caters to high temperature textiles, outdoor products, filtration media, safety spray shields, insulation jackets, awnings and tents, marine applications and boat covers.
15.2.10 Ultra high modulus polyethylene threads Spectra® sewing thread is manufactured from high density polyethylene. Spectra® fibre is one of the world’s strongest fibres (30 cN/denier), up to 10 times stronger than steel by weight and up to 40% stronger than aramid. Spectra® is lightweight and floats on water. Sewing threads made from Spectra® are finding applications where chemical and water resistance is required. They have excellent chemical resistance and can withstand a continuous operating temperature of 120°C. They are used in protective clothing, sails, fishing line, marine rope and slings, and work gloves.
15.2.11 Carbon fibre threads Schappe Techniques produces very thin 2 ¥ 1K (67 ¥ 2 tex) carbon sewing thread, compatible with epoxy and epoxy/PU resins and usable in many composite applications such as prepreg (pre-impregnated composite fibres),
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sewing of dry textile structures, non-crimp multiaxial fabric linkage and the creation of a ‘z’ direction in textile structures [20].
15.2.12 Threads for outdoor applications Sun protection textiles are made from coated polyacrylic fabrics. Sewing threads used to join these require good resistance against UV rays, flu gases, nitrogen oxide, sulphur dioxide, carbon monoxide, humidity/hydrolytic effects and the alkaline effects of flue ash. They also must be able to withstand mechanical actions such as tension, pressure, chaffing and bending. Acrylic sewing threads are not suitable due to poor chafing properties (from erosion due to rubbing). The addition of UV absorbers in the coating of sewing threads marginally improves the rate of strength reduction under UV radiation. High tenacity polyester threads were first developed, as they have high UV resistance. A strength loss of 55% for this thread is observed after 1500 sun-hours, which is still sufficient to transmit mechanical forces. Amann developed sewing threads called Tenara® M1000TR (regular) and Tenara® M1000HTR (heavy) made from ‘100% expanded ePTFE’ (extended polytetrafluoroethylene) [1], which are two to three times stronger than standard PTFE threads. Tenara sewing thread has a slightly lower breaking strength than conventional polyester threads, but does not lose any of its strength after prolonged exposure to sun (polyester threads are prone to breaking down after exposure to the environment, thus causing seam breakage). They are water repellent and PTFE’s inherent chemical resistance ensures it will not rot or mildew and prevents deterioration due to cleaning solutions, motor oils and other destructive substances. More importantly, PTFE is unaffected by UV radiation and will not degrade from continuous sun exposure, pollution, rain and snow. This thread had good colour fastness in 12 colours and can sew up to 2800 stitches per minute. Tarpaulins are exposed to more extreme environments. Tarpaulins for marine applications have to protect boats from sun, wind and rain while the boat is docked. Here the seams need to remain steadfast under the most extreme UV conditions while preventing moisture from soaking through. Tenara® M1000TR threads are suitable to work under these conditions. Sewing needles with deep scarf are recommended if there are skipped stitches. The scarf or clearance cut is a recess across the whole face of the needle just above the needle-eye. Its purpose is to enable a closer setting of the hook or looper to the needle to ensure that the loop of the needle thread will be more readily entered by the point of the hook [2]. A scarf with deep cut helps in avoiding skipped stitches. Rasant®, a cotton polyester core-spun thread (water-resistant), has been a reliable product for many years, offering high seam density in this application. This thread gives easy stitching and trouble-free sewing with the smallest possible stitch holes.
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A comparison of strength retention of various threads under sun is given in Table 15.4 [1].
15.2.13 Threads for airbags Polyester and PA 66 threads are used for most of the sewing operations in airbag production. Airbags used in cars are made from PA 66 fabrics coated with a thin silicone layer. Seams which have to withstand extreme temperatures near the opening of the generator are made with aramid threads. Airbag threads have to be audited according to various standards by airbag manufacturers before they are allowed to be used. Sewing is carried out by multi-directional sewing rigs. It is advisable to use a bonded thread, rather than a twisted thread, when seaming a tight radius airbag air exit hole. Gutermann’s monocord sewing thread (bonded with PA) is made from PA 46 filaments which are easy to twist and dye. The melting point of PA 46 filaments is higher than those of polyester and PA 66, which ensures additional safety. Airbags are inflated during accidents, requiring no skipped stitches. The selection of needle size and throat plate is important. A spun thread with a thermoplastic elastomeric coating can be used for seams joining two fabric panels together to create an airbag. The seam can be heated after assembly of the airbag, such that the thermoplastic elastomeric coating fills in any needle holes. A general comparison of the different raw materials and properties required for an airbag is given in Table 15.5 [21].
Table 15.4 Strength retention of sewing threads outdoors
% Retention of strength under sun after
First year
Polyester/cotton 100% polyester Acrylic Extended PTFE
18 5 2 35–38 23–35 15–25 65 43 40 100 99 99
Second year
Third year
Table 15.5 Comparison of fibres for sewing of airbags
PET
PA66
PA6
PA46
Melting point Strength Elongation Heat durability Cost
Normal Normal Low Normal Low
Normal Normal Normal Normal Normal
Low Normal High Low Low
High Normal Normal High High
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15.2.14 Threads for geotextiles Geotextiles are fabricated in rolls of finite length and width. For installations requiring a large area of geotextile coverage, adjacent rolls must be overlapped or joined. During the construction of roads, railways or pavements, native materials (rock or earth) are levelled to a specific slope underneath the construction. These are called sub grade soil. Depending on the strength of sub grade soil, the amount of overlap is decided. Normally a sewn seam will require only a few inches of fabric from each roll, compared to an overlap which may use two to three feet of material. Both woven and non-woven geotextiles can benefit from using sewn seams. In geotextile applications, the seam is a critical component in forming a wider fabric from the available narrow fabrics. The sewing thread will be exposed to the same environmental conditions as the geotextile and must therefore have similar or better durability under those conditions. This can be important in landfill applications, for example, where both the fabric and thread must be resistant to chemical attack and ultraviolet degradation. Since polyester and polypropylene are the principal materials used for geotextiles, sewing threads are also made from these fibres. For demanding applications, Kevlar is used [22]. Proper selection of the thread size and type is important, since the seam will be no stronger than the thread used to form it.
15.2.15 Threads for antistatic safety workwear Safety workwear is a uniform to safeguard the worker against ignition and explosion in the workplace. Milaine Thunderon SP, a sewing thread manufactured by the Niho Sanmo dyeing company, has an electro-conductive acrylic fibre containing copper sulphide at the surface (10%). The core consists of polyester or polyester-cotton blends. The thread prevents garments clinging to the body, stops soil caused by absorbing dusts and reduces unpleasant sounds when taking the garments off. This thread works as an earth for the human body even during dry weather. It is recommended that this thread be used as a safety stitch needle thread or looper thread for skirts and slacks [23].
15.2.16 Applications of various sewing threads in non-medical technical applications Technical sewing threads are used in numerous applications. The list of applications for any particular thread is ever growing, so drawing up an exhaustive list of applications for all threads is almost impossible. However, the major applications of various sewing threads are listed in Table 15.6.
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Table 15.6 Technical sewing threads in non-medical applications Fibre
End uses
Spectra Kevlar spun
Protective clothing, sails, fishing line, work gloves Seating (aircraft, public), heat-protective clothing, heatresistant shoes, bags, covers, heat- and cut-resistant work gloves, bulletproof vests, hot gas filters Kevlar Airbags, filters, conveyor belts, geotextiles, ballistic clothing, fire suits, wire and cable applications, heat-protective workwear and shoes, bags, covers, gloves, hot gas filters Steel/Kevlar Space shuttle Nomex Airbags, aircraft seats, filter bags, ballistic clothing, fire suits, gloves, shoes, wire and cable applications, hot gas filters Nomex-spun Aircraft seats, fire suits and gloves, hot gas filters E-glass coated with Decorated fabrics, fire-safety textiles (extreme heat up to PTFE 760°C) and filters Basalt Extreme heat and flame application (protective clothing, filtrations) Asbestos Heat protection (extreme heat) Ceramic/rayon Sewing high-temperature parts, heat-protection application such as custom blankets, seals, gaskets, etc. ePTFE Outdoor (awnings/sunblinds, tents, garden umbrellas), chemical filtration, marine applications, geotextiles, heatprotective workwear PTFE Filtration, protective clothing, marine PEEK Container bags, geotextiles, filtration Nylon66 Blankets, curtains, draperies, flags and banners, footwear, monofilament upholstered furniture, handbags, lampshades, luggage interior, luggage, canvas Nylon66 monocord Automobile seat covers, airbags, seat belts, blankets, book bags, handbags, book bindings, brooms, conveyor belts, dyers and finishers, flags and banners, footwear, upholstered furniture, gloves, hammocks, handbags, lampshades, leather belting, luggage, sporting and athletic equipment, quilts PA46 monocord Airbags Acrylic monocord Safety belts, suitcases, shoes, leather and plastic goods Thunderon spun Electro-conductive and antistatic safety workwear Polypropylene Filter and woven bags, geotextiles, pool covers, bulk containers Polyester high Awnings, airbags (bonded threads), brooms, banners, canvas, tenacity filament conveyor belts, car seats, dyers and finishers, flags, filter bags, footwear, geotextiles, safety belts, sails, suitcases, shoes Polyester coreAwnings, sun blinds, boat covers, bulletproof vests, flags, spun tents, canvas, footwear Polyester Automotive interiors, canvas goods, flags, shoes, sporting monocord goods, upholstered furniture Polyester spun – Caskets, lampshades, tents, tarpaulins high tenacity Polyester airFleece goods, flags, mops, upholstered furniture entangled
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Table 15.6 Continued Fibre
End uses
Polyester airtextured Core-spun polyester/cotton Acrylic filament Cotton Cotton blends
Furniture, container bags
15.3
Boat covers, book bindings, flags, tarpaulins, tents Filtration Tea bags Tents and tarpaulins
Surgical threads/sutures for medical applications
15.3.1 Introduction Doctors use a surgical thread, called a suture, in patients to hold soft tissue together while the tissue heals, whether from a deep cut or from a surgical incision to repair damaged tissue. The successful outcome of any surgery depends not only on the surgeon’s skill and the condition of the patient, but also crucially on the optimal characteristics of a carefully chosen surgical suture. Sutures are used mainly for sewing or suturing together the edges and surfaces of tissue, for stopping blood flow, to facilitate wound healing, to reduce the dead space between the tissue surfaces within a wound, and to give stability. Sutures are either interrupted (each stitch tied separately) or continuous (the thread running in a series of stitches, only the first and last of which are tied). Sutures are designed to meet many different requirements. Each surgical procedure needs sutures with specific qualities. In general, the ideal sutures should have the following characteristics [24]: ∑ ∑ ∑ ∑ ∑ ∑ ∑
Smoothness – the suture should cause minimum tissue drag and no damage to the delicate, newly healing tissue during removal. Low capillarity – an ideal suture should not have a wicking effect. Maximum tensile strength. Handling of the suture should be as easy as possible – minimum memory and excellent knot security of the suture are crucial for optimum tissue sealing. An ideal suture must have consistent and predictable performance, and cost effectiveness. The suture must be able to resist bacterial infection. The suture should cause minimal tissue injury or tissue reaction (i.e., be non-electrolytic, non-capillary, non-allergenic and non-carcinogenic).
In the United States, suture manufacturing processes come under the
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regulatory control of the Food and Drug Administration (FDA), under the classification of ‘medical devices’. Sutures are subject to strict quality control; guidelines for quality control are laid down by independent organizations such as the United States Pharmacopoeia (USP) or British Pharmacopoeia (a compendium officially recognized by the FDA). Manufacturers must comply with specific Good Manufacturing Practices (GMP), and ensure that their products are safe and effective. In this section, various types of surgical sutures currently in clinical use are discussed, as well as their limitations and associated problems, and the ongoing research initiatives undertaken to abate those shortcomings.
15.3.2 History The origins of surgery can be traced back many centuries. In the tenth century bc, in India, physicians used to hold an ant or beetle over a wound until it seized the wound edges in its jaws; the insect was then decapitated and its death grip kept the wound closed. Through the ages, practitioners have used a wide range of materials and techniques for closing tissue, namely flax, jute, hemp, silk, cotton fibres, grass, human or animal hair, animal sinew, pig bristles, etc. Catgut sutures gained major popularity during the middle ages, at which time the intestines of goat, sheep and cows were used to make the strings of musical instruments; the name ‘catgut’ possibly developed from the ‘kit’, or resonance chamber, of musical instruments. In about 1800, the development of non-absorbable (silk) or absorbable sutures was begun, with catgut still the most common absorbable suture in use. Surgeons used to pre-sterilize the tough membrane of sheep intestines and applied them by threading through the eye of the needle. Joseph Lister (1827–1912), a British physician, was one of the pioneers of sterilization of sutures (by dipping them in phenols, or a mixture of olive oil and carbolic acid) and also of ‘dissolving’ sutures. A hygienic twisted cord catgut suture manufacturing process was developed by the famous German surgeon Franz Kuhn (1866–1929) [25]. Cow or sheep intestines were collected from the slaughterhouse and only the ‘best’ intestines were chosen for production of surgical catgut. Shortly after removal and before starting the production process, the intestines were washed for the first time in a disinfecting solution containing iodine. The ilium and jejunum portions of the intestine were split into two or more longitudinal ribbons, and the mucosa muscularis and other unwanted layers were removed by chemical and mechanical treatment, before immersing again in the disinfecting solution. The cords were then soaked for 3–4 days in calcium carbonate, washed in water, and immersed for a further 8 days in an iodine solution. The intestines were twisted into cords using a special rotary desk.
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Advances following World War II brought a wide range of other improvements including designs to make forged metal needles attached to suture filaments. The suture thread was fitted into the hollow end of the needle, allowing it to pass through tissue without the double loop of thread that existed on a conventional needle, reducing tissue trauma. The FDA began requiring approval of new suture material in the 1970s. A Medical Device Amendment was added to the FDA in 1976, and suture manufacturers have been required to seek pre-market approval for new sutures since that time.
15.3.3 Classification There are many kinds of sutures, with different properties suitable for various uses. Sutures are available as monofilaments, as braided monofilaments, or as twisted multifilaments, the particular suture being chosen depending on the surgical operation and tissue location. Other sutures, known as pseudomonofilaments, have a braided or twisted core within a smooth sleeve of extruded material. A monofilament passes smoothly through tissue and thus causes low tissue drag but may encounter slippage in knot tying. Braided or twisted sutures can have higher tissue drag (and are usually coated in order to reduce this) but are easier to knot and have greater knot strength. However, braided sutures create a greater response from the body, and should not be used in contaminated wounds, as they may contribute to infection. Sutures can be divided into the following groups: (i) According to their composition and origin: either natural or man-made polymers. Natural sutures are based on natural polymers derived from animals or plants. Man-made sutures are produced from synthetic polymers similar to the processes used in synthetic fibre production (melt, dry, wet spinning). (ii) According to their configuration: either monofilament or multifilament. Multifilament sutures consist of several twisted or braided monofilaments. (iii) According to their absorption ability: either absorbable/biodegradable or non-absorbable/non-biodegradable. Absorbable sutures An absorbable suture decomposes in the body relatively quickly (within days) compared to non-biodegradable sutures, degrading as the wound or incision heals. These types of sutures are generally used internally or on parts of the body that heal quickly.
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A few examples of absorbable sutures are listed in Table 15.7. They include plain gut (from catgut, i.e. dried and treated bovine intestine) and chromic gut, as well as polyglactin (‘Vicryl’), polyglycolic acid (‘Dexon’, a glycolide–lactide copolymer) and polydioxanone (a copolymer of glycolide and trimethylene carbonate sutures). A polyglycolic acid-based suture, Dexon II, is used for deeper layers and in children as a subcuticular suture. It is generally not recommended for the skin as it is absorbed by hydrolysis. These different polymers are marketed under specific trade names. Organic sutures are broken down by enzymatic processes, whereas the synthetics are broken down via hydrolysis. Absorbable sutures are made from either collagen or synthetic polymers. Collagen sutures are derived from purified connective tissues from the submucous layer of sheep’s or beef’s (bovine) intestines. Once cleaned, they are dried and twisted into threads of various sizes. This collagenous tissue is treated with an aldehyde solution to block the NH2 groups in the collagen, which crosslinks and strengthens the suture, thereby increasing its resistance to enzymatic degradation. Suture materials treated in this way are called plain gut. During the grinding and polishing steps in the manufacturing process, catgut sutures can form an unpredictable number of weak points, resulting in fraying and fibrillation. Catgut can cause tissue reaction and inflammation during degradation. If the suture is additionally treated with chromium trioxide, or soaked with chromic acid salt, it becomes chromic gut, which is more highly crosslinked than plain gut. This process helps to increase the half-life of degradation and increase the tensile strength. Plain catguts maintain significant tensile strength for only 5–6 days, and Table 15.7 Absorbable sutures Generic name
Raw materials
Natural 1. Plain catgut 1. Submucosa sheep intestine 2. Chromic gut 2. Serosa of beef intestine + buffer chromicizing 3. Collagen (plain and chromic) 3. Beef flexor tendon Synthetic 1. Polyglycolic acid 2. Polyglycolic acid 3. Polyglactine (Vicryl)
4. Polydioxanone (PDS)
5. Polyglyconate (Maxon)
1. Homopolymer of glycolic acid 2. Homopolymer of glycolic acid coated with polycaprolate 3. Copolymer of lactide–glycolic acid coated with calcium stearate, polyglactine 370; braided 4. Polymer of paradioxanone; monofilament (less affinity for bacteria, higher dissociation time, but stiff, difficult to tie) 5. Copolymer of trimethylene carbonate and polyglycolic acid; monofilament, better tying
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stop providing wound security in 2 weeks. Chromic catgut can maintain its tensile strength for almost 20 days. As foreign proteins are not directly exposed, chromic catguts present less risk of inflammation and foreign body reaction compared to plain catguts. Plain gut and chromic gut sutures are composed of several plies that have been twisted slightly, machine ground and polished, yielding a relatively smooth surface that is monofilament-like in appearance. In most locations of the human body, the degradation of absorbable sutures is initiated by acid phosphatase. Aminopeptidase, beta-glucoronidase (released by macrophages) and leucine aminopeptidase (released by neutrophils) play important roles later in the absorption period. Collagenase is also thought to contribute to the enzymatic degradation of collagen sutures. Because the absorption of plain gut and chromic gut occurs by enzymatic degradation, it is very difficult to indicate the exact designation of a consistent absorption time. In addition to their unpredictable absorption time, natural fibre absorbable sutures have several other distinct disadvantages: first, they have a tendency to fray during knot construction; second, there is considerably more variation in their retention of tensile strength than is found with synthetic absorbable sutures. Today, most developed countries have banned the use of catgut, and synthetic absorbable sutures are more commonly used. Ethicon, Inc. (USA) developed Polyglactine 910 (a copolymer of lactide–glycolide), sold under the commercial name of Vicryl. Original Vicryl was a braided structure, which could maintain 50% of its tensile strength in tissue for 30 days, but this version is no longer available, as it has been replaced by Teflon-coated Vicryl. Development of such synthetic degradable sutures was definitely a major step forward from catgut, as evidenced by the enhanced success of clinical outcomes. Wetter et al. [26] reported that in appendicectomies (surgical removal of the vermiform appendix) the incidence of wound infection with Vicryl was less frequent than with even chromic catguts. In 1983, Ethicon developed polydioxanone (PDS), made from paradioxanone. Unlike Vicryl, it is a monofilament suture. On one hand, it has inherently less affinity for bacteria due to its chemical composition; on the other hand, it is quite stiff and difficult to handle and tie. Scar spread was reported to be less with PDS than with Polyglactin 910 [27]. One of the most developed absorbable synthetic sutures is polyglyconate (trade name Maxon), made up of a copolymer of trimethylene carbonate and polyglycolic acid. It is a linear copolymer made by reacting trimethylene carbonate and glycolide with diethyleneglycol (as an initiator) and stannous chloride dehydrate (as the catalyst). Maxon’s handling and tying characteristics are far superior to those of Vicryl and polydioxanone, but there is no significant difference in post-operative complications. The progressive loss of Maxon’s tensile strength and eventual absorption occurs by means of hydrolysis.
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Absorption of Maxon sutures reaches a minimal level approximately 2 months after implantation and it is generally completely absorbed within 180 days. Scientists have developed sutures from bovine serum albumin (BSA), a plasma protein which is one of the most abundant proteins in the human body. BSA is already produced on a commercial scale (for applications in biochemistry) and the immune system does not recognize it as an artificial protein; this reduces the risk of inflammation in the wound. However, BSA does not yet come in filament or yarn form. Attempts have been made to convert BSA into nano-fibres, by electrospinning [28], which could finally be made into threads. These threads are expected to reduce the scarring left when stitches are removed. More significantly, as they do not provoke inflammation, they might be used to repair the wounds of patients with conditions such as diabetes, in which chronic skin infections often get in the way of healing when normal stitches are used. But the unavoidable risk of disease transmission from animal to human is always an obstacle to this approach. Non-absorbable sutures Non-absorbable sutures do not break down and must eventually be removed by a surgeon after a surface incision has healed. These types of sutures are best for slower-healing body tissues. They include silk, linen, cotton, polyester (Ethibond, Tevdek), stainless steel wire, polypropylene (Prolene, Fluorofil), polyethylene, proprietary nylon sutures (Ethilon, Nurolon), polyethylene terephthalate, polybutylene terephthalate, polyester, polyamide and Goretex. Raw materials and generic names are shown in Table 15.8. Nylon sutures are available in monofilament, multifilament and braided forms. Braided sutures are relatively inert in tissue and possess the same handling and knot construction characteristics as silk sutures. Nylon sutures have a high tensile strength and low tissue reactivity, degrading in vivo at a rate of about 12.5% per year by hydrolysis. They are more pliable than polypropylene and are therefore easier to handle, and are thus favoured for the construction of interrupted percutaneous suture closures; however, nylon sutures have higher drag with tissue than polypropylene. The main disadvantage of nylon suture is that knot untying can cause cutting in tissues, so a triple knot must be tied. The most commonly used nylon sutures are fine, with sizes of 4/0 to 3/0; finer sutures break easily when applying too much tension to the wound edges. Polypropylene sutures have inherent smoothness, which makes them easy to tie and simple to remove. Polypropylene sutures encounter lower drag forces in tissue than nylon sutures, accounting for their frequent use in continuous dermal and percutaneous suture closure. On the other hand,
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Table 15.8 Non-absorbable sutures Generic name
Raw materials
Natural fibres 1. Surgical cotton 2. Surgical linen 3. Virgin silk; surgical silk Synthetic fibres 1. Nylon
2. Polypropylene (Prolene) 3. Polyester 4. Ethibond
1. Twisted natural cotton 2. Twisted long-staple flax 3. Natural as spun, untreated; twisted, siliconimpregnated 1. Polyamide 6,6 monofilament; Polyamide 6,6 braided; polyamide 6 twisted fibres enclosed in a polyamide sheath; polyamide 6,6 silicon treated 2. monofilament; stiff, untying of knot, cutting of tissues 3. monofilament, braided, silicon treated, tefloncoated 4. Polyester coated with polybutylate
their low coefficient of friction facilitates knot rundown, and suture passage through the tissue results in low knot security (knots have a tendency to slip). A new polypropylene suture has been developed that has increased resistance to fraying during knot rundown, especially with smaller diameter sutures. Polypropylene sutures are extremely inert in tissue and have been found to retain tensile strength in tissues for as long as two years. Polypropylene sutures are widely used in plastic, cardiovascular, general and orthopaedic surgery. Sutures such as Surgilene or Prolene are best suited for subcuticular and continuous type suturing. These are the easiest to pull out.
15.3.4 Size/gauge system Sutures are sized according to a system developed by the USP and are numbered on two scales depending on whether the suture is large or small: ∑ ∑
A whole number system for larger sutures, from 5 (largest) to 0 (smallest). Size 0 has a diameter around 0.30–0.39 mm. Size 5 has a diameter of 1.00–1.09 mm. A composite number system for sutures smaller than 0, from 1/0 (largest) to 11/0 (smallest). These are ‘aught’ sizes; e.g., 11/0 is pronounced as 11-aught. Size 8/0 has a diameter of 0.05–0.069 mm.
Larger sutures (2 and up) are used for jobs like abdominal repair, 2/0 to 5/0 are used for stitching on skin, while smaller sutures (5/0 to 11/0) are used for repairing fine blood vessels, microsurgery and stitches on the eyelid and eyebrow. The smallest possible sutures should be used to minimize scarring. Another important factor is that the incidence of inflammatory reactions
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can depend on the surface area of the suture in contact with the tissue. The guiding principle is always that the smallest gauge capable of supporting the wound should be used. A larger sized suture than needed does not provide any better wound support but can increase the potential for problems related to inflammation.
15.3.5 Manufacturing process A wide variety of sutures have been developed in order to satisfy the requirements of modern surgery. Suture manufacturers try their best to provide surgeons with sutures which are as close as possible to ‘ideal’, though such ideal sutures are still a future dream and a much sought-after target for scientists. Suture manufacture typically consists of three stages: (i) production of the sutures themselves, (ii) production of needles and (iii) a finishing process that attaches needles to the sutures, packages, and sterilizes. The manufacture of sutures for surgical use is not very different from the production of typical synthetic filaments, in that it involves extrusion of the polymer filament, then drawing/stretching and heat-setting (Fig. 15.3), resulting in either a monofilament or a multifilament, which is then braided or twisted. The chemical composition and concentrations of additives can govern the microstructure (orientation, morphology and crystallinity) and the chemical structure (branching, crosslinking, molecular mass distribution) and hence, ultimately, dictate the long-term performance of the viscoelastic material. The number of filaments braided together varies from 20 to a few thousand, depending on the size of the suture to be made (Fig. 15.4). The braided or twisted structures are stretched by up to 20%, passed over a hot plate to iron out any imperfections present, and then hot annealed (for a few minutes to several hours) under taut conditions, depending on the type of suture being made. Biomechanical studies demonstrate that the manufacturing process (i.e., annealing, relaxation) can dramatically influence the surface characteristics of the suture without altering its strength. Such changes in the surface characteristics can facilitate knot construction of the suture. After annealing, the suture may be coated. Coating materials vary depending on what the suture is made from. Sutures are tested for their quality, i.e., their length, strength, defects and dissolvability in animals or in test tubes (for absorbable sutures), and then passed on to the process called ‘swaging’, which consists of cutting the sutures into standard lengths, and mechanically inserting the cut lengths into the holes of the needles. The length of sutures (usually 18 inches or more) depends on the character of the work and nature of the operation they are intended for; deep work in the pelvis, for example, requires a much longer suture than would be necessary in suturing a wound in an area closer to the surface.
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(a)
(b)
15.3 (a) Typical manufacturing process of synthetic polymeric monofilament suture; (b) drawing and heat-setting step of making suture from thermoplastic polymer.
Polyester sutures were the first synthetic braided suture material shown to last indefinitely in tissues. They have satisfactory tensile strength, minimal tissue reaction, maximal visibility, and non-absorbent and non-fraying qualities. Their acceptance in surgery was initially limited because they had a high coefficient of friction that interfered with the suture’s passage through tissue and with the construction of a knot. When the sutures were coated with a lubricant (markedly reducing the suture’s coefficient of friction), polyester sutures gained wide acceptance in surgery. Polyester sutures are often coated with silicone, polybutylene adipate or Teflon. However, fragments of these coatings can tear and migrate into surrounding healing tissues, provoking inflammatory reactions. In the polyester suture Ethibond, where polyester is coated with polybutylene, a natural affinity exists between the coating and the polyester suture filaments, eliminating such problems. The expanded polytetrafluoroethylene (ePTFE) suture is porous with
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15.4 Braided suture showing less memory.
50% porosity. The porous nature of the suture allows tissue ingrowth into the suture. The ePTFE suture has some novel performance characteristics that are distinct from those of other monofilament non-absorbable sutures: ePTFE is over 100 times more supple than any other monofilament suture, without evidence of plastic memory; additionally, the rate of creep (suture elongation that occurs when a suture is subjected to constant load for an extended period) encountered in an ePTFE suture is significantly less than that of a polypropylene suture. However, the breaking strength of an unknotted and a knotted ePTFE suture is significantly less than that of a polypropylene suture. For a polypropylene suture, three throws are required to form secure square knots; an ePTFE suture requires seven throws to form the same knot. Silk sutures are made from degummed silk filaments that are twisted or braided. Braided sutures are coated uniformly with a special wax mixture to reduce capillarity and to increase surface lubricity, which enhances handling characteristics, ease of passage through tissue, and knot rundown properties. Sometimes silk thread is pretreated with aluminium acetate to fix the wax and to retard the loss of wax during sterilization. Encasing twisted silk fibres within a non-resorbable coating of tanned gelatin prevents cell attachment or tissue ingrowth. Silk suture has high tensile strength and is relatively inexpensive but often causes tissue reaction. Linen sutures are made by twisting linen strands to give them sufficient strength. Cotton sutures are made by twisting cotton yarns and were used
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for both internal and external sutures, always used wet for maximal strength. However, these are not used any more. Wire sutures are metallic and derived from stainless steel. They are available in both monofilament and multifilament forms, have maximal flexibility and tensile strength, yet cause little or no local reaction in the tissue in which they are placed. Flexon sutures, made by Davis & Geck, are twisted multifilaments. Despite their excellent knot security, stainless steel sutures are not particularly popular with surgeons due to the difficulties in handling them, as they are susceptible to kinks. New suture designs are tested by subjecting them to chemical tests, such as soaking them in various solutions, and by testing on animals. Sutures may also be dyed to make them easy to see during surgery; only approved dyes and coatings should be used on sutures. Absorbable coatings include Poloxamer 188 and calcium stearate with a glycolide–lactide copolymer. Non-absorbable sutures can be coated with wax, silicone, fluorocarbon or polytetramethylene adipate. Various suture accessories are associated with the suture manufacturing industry (Fig. 15.5). Suture needles are made of stainless or carbon steel and sometimes electroplated. Suture anchors are threaded fixation devices designed to maximize the anchorage of sutures at the implant or bone interface by being screwed into the bone. They can be made of metal or biodegradable materials. It is important to pay attention to the friction between needles and anchors and sutures, since breaks most commonly occur at junction points. Packaging materials include water-resistant foil, such as aluminium foil, as well as cardboard and plastic. Sutures, already attached to a needle, are packed into foil packs and sterilized to kill all microbes. Traditional methods of sterilization include dry heat or moist heat sterilization, exposure to ethylene oxide in a fixed chamber, radiation (gamma and electron beam), liquid chemical sterilants for sterilizing single-use devices, exposure to ultraviolet light, and combined vapour and gas plasma.
15.5 Suture accessories: needle and anchor.
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In the case of sutures that can withstand gamma radiation, the sealed foil pack is put inside a cardboard box and set on a conveyor belt so that it passes under lenses emitting gamma radiation. Commonly used ionizing radiation consists of high-energy electrons and Co-60 irradiation with a dosage of around 2.5 megarads (1 rad = 6.2 ¥ 1023 eV g–1; 1 Mrad = 106 rad). For some sutures, this process can lead to degradation of the polymer chain, to crosslinking or discoloration. Chain breaking or crosslinking can cause significant modulation in the suture’s mechanical properties. Nylon, polyester and polypropylene sutures show minimal strength loss after irradiation sterilization. (For sutures that cannot withstand gamma radiation, the foil pack is left open and put inside a chamber which is then filled with ethylene oxide gas; the foil packs are then sealed and packaged.)
15.3.6 Characterization The characteristic features of suture materials, which govern the overall performance of sutures during the wound closure process and post-operative stages, fall into the following categories: ∑
Physical characteristics which govern basic information about the suture material, and which can in turn affect mechanical and biological interactions between suture and tissue. ∑ Handling characteristics which determine the mechanical behaviour of the suture before, during and after wound closure. ∑ Biological characteristics which define the biological response in a patient’s body after implantation. Biocompatibility includes issues such as inflammatory reaction, propensity towards infection, carcinogenicity, allergy etc. A suture is a foreign material to the body; the tissues surrounding the suture can be affected by it and they can affect the properties of the suture itself. Physical characteristics The USP and the British Pharmacopoeia formulated a set of definitions and standards which provide benchmarks for suture testing and requirement limits for suture quality. As dictated by the USP, a suture must comply with their standard limits regarding suture length, size (diameter), knot-pull strength, and needle attachment force. Knot-pull strength, as defined by the USP, is a standard parameter for defining the limits of suture knot failure. Knot-pull strength is measured in kilograms. This parameter is measured on a tensilometer after a simple knot has been made around a rubber tube of standard dimension, and tensile stress is applied to the knot’s end until it breaks. Typical knot-pull strength limits are around 0.005 to 9 kg. © Woodhead Publishing Limited, 2010
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Needle attachment force is defined as the force required to separate a needle from a suture. The needle and suture’s ends are gripped with opposite clamps on a tensilometer and tensile stress is applied. Needle attachment force can vary from 0.007 to 1.8 kg for various commercially available sutures. One very important physical property, knot security, is one of the main parameters that govern final knot performance. A secured knot is defined as one that, when tested to failure, breaks rather than unties by slippage, and this indicates how well the knot will stay in position. Knot security is dependent on two parameters: knot tie-down, which defines how easily a surgeon can slide the knot down to the wound edge, and tissue drag, which describes how easy it is to pull a suture both during wound closure and its removal after the wound is healed. Hence, knot security is defined as the effectiveness of the knot at resisting slippage when load is applied, and is dependent on friction, internal interference and slack between throws. The security of any tied suture can also be improved by the use of certain patterns in stitching. The friction factor is affected by the size of the contact area between threads, the tightness of tying, and the suture material used. A patient’s life may depend on the security of one ligature. Slippage of a tie may result in a life-threatening haemorrhage. A suture with low knot security may easily untie, causing wound reopening (dehiscence). Hanna et al. [29] developed a reliable method for testing knot-security and studied 2700 endoscopically tied knots with a tensiometer which used a computerized algorithm to develop an index of knot quality. Many others have also used tensiometers to study the distraction forces of surgical knots [30–33]. Knot security depends upon the chemical composition of the suture, knotting techniques, the friction coefficient, compressibility, stiffness, etc. Generally, uncoated sutures have higher knot security than coated ones. The two most common types of knots used in surgery are ‘square knots’ and ‘sliding knots’, with square knots being more secure than sliding knots [34]. A few other critical physical parameters, such as elasticity, plasticity, memory and capillarity, can have significant influence on the final performance of a suture. Elasticity is defined as the ability of the suture to return to its original state after stretching. Plasticity of the suture is its ability to retain its new, deformed state. Memory depends on the elastic–plastic properties of the suture material; this is crucially important in governing a suture’s tendency or ability to return to its previous shape. Sutures with high memory (e.g. nylon) tend to untie, hence their knot security is quite low; sutures with low memory (e.g. silk) have fewer tendencies to untie. High memory sutures can even have packaging memory, which is the tendency of a suture to regain the spiral form it had inside its packaging. Suture strength should ideally match the in vivo tissue strength. The tensile strength of a suture is a complicated issue. The tensile property of a
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straight suture is one of its fundamental mechanical characteristics; however, depending on the type of knot chosen, results could be drastically different from the mechanical property measured using a straight suture filament. The need for systematic study of the tensile properties of suture materials, such as stress-strain curves, elastic modulus, work on ruptures and stress–relaxation comparing straight filaments and knotted sutures, is critical to generate better understanding. Another important physical property, capillarity, is affected by the configuration of the suture (i.e. whether it is a monofilament or multifilament). Capillarity is the action by which pores in a solid transport liquid on contact, so that tissue fluids transfer from the wet end of the suture to the dry end. The excess surface energy of a solid over that of a liquid determines the contact angle, i.e. its hydrophilicity. The product of the surface tension of the liquid and the cosine of the contact angle decides the kinetic of liquid transport. Smooth monofilaments exhibit very little capillarity on their surface pores. Braided and twisted sutures have many interstices and, if they are made of natural fibres, provide high fluid absorption, i.e. they can transport fluids or microorganisms found in tissue. Thus, the possibility of the growth of bacteria is enhanced with a higher capillary suture. Handling characteristics A suture’s physical and mechanical properties include its form, its diameter (and its variation), its length, how well the needle is attached to the suture, its breaking strength, breaking elongation, modulus of elasticity, bending rigidity, creep, stress relaxation, friction coefficient, capillarity and swelling. Handling characteristics define the behaviour of a suture before and after the knot has been tied. Handling properties include pliability, flexibility, smoothness, packaging memory, knot tie-down, knot slippage/security and tissue drag. The knottability of a suture is defined as the ability of the suture to be tied with relative ease by surgeons, and the difficulty of unknoting it. Knottability of a suture cannot be evaluated by any single parameter as it encompasses a constellation of handling characteristics, such as pliability or flexibility (the ease with which a suture can be bent), smoothness, the coefficient of friction, memory and knot security. Knottability improves with decrease in stiffness. Stiff sutures need larger loops and are thus more difficult to knot. In a continuous suturing technique with small loops, a stiff suture would act like a spring due to its tendency to relax from small loops and, as a result, would eventually pull the wound edges apart rather than closing them together (Fig. 15.6). Hence, flexible sutures are generally preferred. Sutures are packed after inserting them into a needle. They develop kinks due to prolonged stay in the pack. The ability of the sutures to retain
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15.6 Opening up of wound, due to improper selection of stiff suture, can cause delay in wound healing.
these kinks (‘memory’) hinders the surgeon’s ability during wound closure, particularly when tying the knot, as the knot tends to untie. Sutures should have low memory. Thermoplastic fibre sutures such as nylon (Fig. 15.7), polyester and polypropylene have very high memory (except for ePTFE sutures). Monofilaments have higher memory than braided ones, since the frictional forces between the constituents of the braid bind them upon straightening the suture after unpacking (Fig. 15.4). Braided sutures generally have higher flexibility and lower memory and handle more easily than monofilaments of the same size. There are fewer reports of monofilament sutures causing infection since, due to the absence of interstices, microbial organisms are prevented from being harboured, resulting in decreased risk of inflammation. Biological characteristics The chemical composition of suture material should be selected in such a way that it does not cause toxicity in the body after biodegradation. The materials should not, either directly or through the release of their material constituents, produce adverse local or systemic effects, or be carcinogenic. Any suture is a ‘foreign’ material implanted in the human tissue; hence there is always a chance of eliciting inflammatory immune reaction to the suture. Inflammation can occur, depending on the chemical ingredients of the suture material and its physical configuration. To approve a new absorbable suture, the FDA needs the documentation of the biodegradation or resorption profile
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15.7 Monofilament nylon suture showing high memory, resulting in low knot security that will cause undesirable wound edge opening (dehiscence).
of the final sterilized suture in vivo or in vitro, as a function of the residual tensile strength of the suture for a clinically significant period of time. The numbers of sutures tested should be sufficient to demonstrate the consistency of the surgical suture’s tensile strength retention. This usually involves testing at least the largest and smallest sizes of suture, plus a selection of the sizes in between, skipping no more than two size differences between those sizes tested. FDA recommendations for requirements for the biological evaluation of sutures are described in ‘Use of International Standard ISO10993, Biological Evaluation of Medical Devices, Part 1: Evaluation and Testing’ [35]. Measurement of the in vivo degradation of sutures separates them into two general classes: sutures that undergo rapid degradation in tissues, losing their tensile strength within 60 days, are ‘absorbable sutures’; those that maintain their tensile strength for longer than 60 days are ‘non-absorbable sutures’. This terminology is somewhat misleading because even some non-absorbable sutures (e.g. silk, cotton and nylon) lose some tensile strength during this 60day period. Compared to the implanted non-absorbable sutures, silk sutures retain 50% of its tensile strength at the end of the first year, and none after
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two years. Cotton retains 50% of their strength in six months and 30–40% at the end of two years. Nylon retains approximately 25% of its original strength throughout the two-year observation period. Synthetic absorbable sutures are preferable to non-absorbable sutures. Uncoated sutures cause less foreign body reaction than coated sutures. Fragments of coating materials can form microparticles and migrate to neighbouring tissue. Another critical aspect of biological evaluation is propensity of infection due to configuration of the suture. The simple act of piercing the skin during suturing opens up avenues for infection, through which opportunistic bacteria can infiltrate the incision site. Presence of a suture further increases the tissue’s susceptibility to contamination. The sutures least likely to provoke infection are composed of absorbable polymers or non-absorbable nylon and polymers. Non-absorbable Dacron, stainless steel and cotton or silk sutures generally carry a greater chance of infection. Due to the high capillarity of braided sutures, bacteria can hide in the interstices and escape the attack of immune cells. Such bacteria can induce infection after proliferating in the surrounding tissue. Attempts are being made to coat antimicrobial agents on the surface of the suture materials to reduce infection rates. Adhesion of tissues to the suture surface is another commonly reported complication, and hence a source of major concern. Post-surgical adhesions were found to extend either from sutures themselves or from their direct surroundings. During the wound healing process, cells can grow inside the interstices of braided structures. Such tissue ingrowth can cause a major problem during removal of the suture, and can inflict new damage to the delicate healing tissue. The composition and configuration of the suture, as well as the length of the suture cut end, can affect adhesion [36]. Allergy to suture material, especially to catgut, is a well-reported phenomenon. Antibodies to catgut have been detected in patients after surgery. Chromic salts are added to catgut to delay degradation, but can provoke an allergic reaction in patients who are chromate-sensitive. Allergies to nylon suture have been reported during vitrectomy (surgery of the eye), or cataract surgery, and the symptoms of allergy were resolved after removal of the suture. Silk suture has a high propensity to induce severe foreign body reaction or inflammation [37]. The lustrous silk fibre is composed of a fibrous protein (fibroin) core surrounded by a glue-like protein, sericin, probably to protect the cocoon against microbes and predators. In virgin silk filaments, it has been found that, when sericin is attached to the fibres, an inflammatory response (by activation of macrophages) can be induced [38]. Sericin in the presence of lipopolysaccharide shows an inflammatory response by initiating the release of cytokines, such as tumour necrosis, a factor causing native silk fibre-induced immune responses [39, 40]. There are even some reports of type-I (immediate) allergy due to activation of Immunoglobulin E [41]. Detailed understanding of such inflammatory mechanisms is still unclear,
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but one reason could be either that sericin-coated silk fibres provide better adhesion to macrophages, or that the conformational change of sericin molecules on binding to silk fibres primes the macrophages for subsequent stimulation. Fully degummed silk fibres, by contrast, lack the required mechanical strength to be used as surgical suture. All these characteristics need to be considered by suture manufacturers when developing new products, or by surgeons when selecting a suture for a specific type of operation.
15.3.7 Selection of suture There is no single suture possessing all the ideal characteristics. Selection of a surgical suture material for a specific surgery should be based on its biocompatibility and biological interaction with the specific wound, its mechanical performance in vivo and in vitro, and its lack of internal capillarity and wicking effect in wounds. Polypropylene monofilament sutures meet most of these criteria and, further, they have a smooth surface, facilitating easy draw without cutting very tender tissues. They have a minimum reaction to organisms and a high resistance to invasion of tissues into the monofilament; hence they are easily removable even after they have been present for a long time in a wound. Polypropylene monofilaments are easily tied with surgical knots and fibrillate, i.e. they can be deformed and ‘flattened out’ in the zone of the wound, making it possible to fix the position of the knot and increase its reliability. They retain their strength, flexibility and resistance to bending after many years of implantation. Sutures with a high degree of memory, particularly monofilament sutures, are stiff and difficult to handle; the knots are less secure than is ideal and may require an extra throw to prevent loosening. Hence, during wound closure, due consideration should be taken of the type of suture, the tying technique, and the configuration of the suture loops. For example, resorbable monofilament suture material is useful in high pressure vessel systems; usually a 4/0 or 5/0 monofilament suture is used for the stitching of femoral arteries. A polyglycolic acid suture material may be more desirable than non-absorbable suture material in microvascular anastomoses (i.e., in abnormal narrowing of a branched structure, such as in blood vessel networks). Investigation of tissue reactivity to suture materials in microsurgical arterial anastomosis showed [42] that when using sutures with polyglycolic acid and monofilament nylon, tissue reactivity to both types of suture had similar histological characteristics after 40 days of surgery. But, around 40–90 days after surgery, tissue reactivity specific to each type of suture was noticed. In the group using a polyglycolic acid suture, the inflammatory process reduced with absorption of the polyglycolic suture, with full restoration of the vessel wall. But, in
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the second group receiving a non-absorbable nylon monofilament suture, the inflammatory process persisted, causing a fibrosclerotic transformation of the vessel wall.
15.3.8 Future trends Due to the advent of laparoscopic surgery or minimally invasive surgical approaches, one major challenge to the clinicians is how to knot a suture in a confined space during surgery of internal organs. Attempts are being made to develop sutures from shape-memory polymeric materials, which should have the ability to assume multiple shapes according to specific stimulations, such as body temperature, pH of tissue fluid, ionic concentrations in the tissue, etc. The permanent shape of such shape-memory sutures can be substantially different from their initial temporary shape. After insertion in the body, a complex mechanical deformation could be performed automatically, instead of manually, by the surgeon. Multi-block copolymer oligo(e-caprolactone)diol coupled with 2,2(4),4-trimethylhexanediisocyanate has been used to develop smart sutures [43], demonstrating the feasibility of the concept. Such smart degradable sutures, with tailor-made compliance, have the potential to bring a paradigm shift in surgical suture technology. Polymer chemists are still looking for novel materials to develop ‘ideal’ sutures. By using recombinant DNA technology, living organisms such as bacteria can be used to create chemicals that would be difficult to produce under standard industrial methods. The US FDA has recently approved TephaFLEX absorbable suture, the first absorbable polymer suture made from material isolated from bacteria modified by recombinant DNA technology, manufactured by Tepha, Inc., of Cambridge, Massachusetts, USA. The coefficient of friction is a measure of the slipperiness of a suture, affecting the tendency of the knot to loosen after it has been tied; more friction results in a more secure knot. Sutures with a high coefficient of friction (generally multifilament sutures) are easy to handle and manipulate for knot tying. Over the last decade, clinicians have been trying to minimize tissue damage, and achieve better anchorage, by using barbed architectures [44]. Recently, bidirectional barbs have been introduced using micro-machining techniques in a spiral pattern along the circumference of the monofilament suture. A polydioxanone-based surgical suture, developed by Quill Medical Inc., USA, is able to anchor itself in tissue without the need for a suture knot, due to the barbed architectures present on its surface.
15.3.9 Conclusion Industrial sewing threads are premium products achieving high margins for thread producers. However, the cost of thread is still a fraction of that
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of the final sewn product. Thread manufacturers continuously research the development of new industrial threads for various applications. Customers also inadvertently invent new applications for the threads already available on the market. As research progresses in developing new technical fibres, the range of sewing threads catering to existing and new applications is set to grow at a hectic pace. During the past few decades, sutures have been extensively used for surgical wound closure and many related clinical applications. On the basis of their unique performance characteristics, specific sutures are recommended for specific wound closures. However, recently, the concept of suture-less wound closure procedures has gained popularity with the advent of skin staples, adhesive tapes and tissue adhesives as potential alternatives to sutures. These products are still in their preliminary stages. Ongoing research is leading to major advancements in suturing technology with further development of new suture materials.
15.4
References
1. A. Pyper, Technical Text, 1999, 42(2): 17. 2. H. Carr and B. Latham, The Technology of Clothing Manufacture, Blackwell Science, Oxford, 1994. 3. P. Ehrler, Intl Text Bull Nonwovens Industrial Textiles, 1998, 3: 22. 4. M. S. Cooper, Amer Text Inst, 1986, 15(10): 38. 5. J. O. Ukponmwan, A. Mukhopadhyay and K. N. Chatterjee, Sewing threads, Text Prog 2000, 30(3/4), Textile Institute, Manchester, UK. 6. C. Ginnane, Industr Fabric Prod Rev, 1987, 64(7): 48. 7. A. Crook, Textiles, 1991, 20(2): 14. 8. R. S. Rengasamy, V. K. Kothari, R. Alagirusamy and S. Modi, Studies on air-jet textured sewing threads, Ind J Fibre Text Res, 2003, 28(3): 281. 9. http://www.amefird.com 10. http://www. coatsna.com 11. http://www.3m.com/product/information/Nextel-Sewing-Thread.html 12. http://www.jpscompositematerials.com 13. http://www.basaltfm.com/eng/row_basalt.html 14. A. G. Mez, Melliand Textilber (Eng Ed), 1985, 14: 792. 15. http://www.threadsindia.com 16. K. S. Rama Rao and S. K. Raja, Man-made Text India, 1995, 40: 189. 17. K. R. Salhotra, P. K. Hari and G. Sundaresan, Sewing thread properties, Text Asia, 1994, 25(9): 46. 18. A. Wimmer, Chemiefasern/Textilindustrie, 1990, 40(92): E67. 19. http://www.gore.com 20. http://www.netcomposites.com/news.asp?4893 21. E. Lindinger, Technical Text, 1988, 41(11): 51. 22. F. K. Ko, Geotext Geomembranes, 1987, 6: 93. 23. Nihon Sanmo Dyeing Co. Product Guide. 24. M. J. Bojrab et al., eds, General characteristics of suture material, in Current Techniques in Small Animal Surgery, 4th edition, 1998, pp. 19–24.
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25. U. A. Dietz, F. Kehl, W. Hamelmann and C. Weisser, On the 100th anniversary of sterile catgut Kuhn: Franz Kuhn (1866–1929) and the epistemology of catgut sterilization, World J Surg, 2007, 31: 2275–2283. 26. L. A. Wetter, M. D. Dinneen, M. D. Levitt and R. W. Motson, Controlled trial of polyglycolic acid versus catgut and nylon for appendicectomy wound closure, Br J Surg, 1991, 78(8): 985–987. 27. B. Guyuron and C. Vaughan, Comparison of polydioxanone and polyglactin 910 in intradermal repair, Plast Reconstr Surg, 1996, 98(5): 817–820. 28. Y. Dror, T. Ziv, V. Makarov, H. Wolf, A. Admon and E. Zussman, Nanofibres made of globular proteins, Biomacromolecules 2008, 9(10): 2749–2754. 29. G. B. Hanna, T. G. Frank and A. Cuschieri, Objective assessment of endoscopic knot quality, Am J Surg 1997, 174: 410–413. 30. R. P. Brown, Knotting technique and suture materials, Br J Surg 1992, 79: 399–400. 31. S. M. Shimi, M. Lirici, G. van der Velpen and A. Cuschieri, Comparative study of the holding strength of slipknots using absorbable and nonabsorbable ligature materials, Surg Endosc 1994, 8: 1285–1291. 32. E. K. Batra, P. T. Taylor, D. A. Franz, M. A. Towler and R. F. Edlich, A portable tensiometer for assessing surgeon’s knot tying technique, Gynecol Oncol 1993, 48: 114–118. 33. D. A. Franz, E. K. Batra, R. F. Morgan and R. F. Edlich, A portable tensiometer for assessing knot-tying technique, Orthopedics 1995, 18: 555–558. 34. E. J. van Rijssel, J. B. Trimbos and M. H. Booster, Mechanical performance of square knots and sliding knots in surgery: comparative study, Am J Obstet Gynecol 1990, 162(1): 93–97. 35. http://www.fda.gov/cdrh/g951.html 36. E. A. Bakkum, R. A. J. Dalmeijer, M. J. C. Verdel, J. Hermans, C. A. van Blitterswijk and J. B. Trimbos, Quantitative analysis of the inflammatory reaction surrounding sutures commonly used in operative procedures and the relation to postsurgical adhesion formation, Biomaterials 1995, 16(17): 1283–1289. 37. H. K. Soong and K. R. Kenyon, Adverse reactions to virgin silk sutures in cataract surgery, Ophthalmology 1984, 91: 479–483. 38. B. Panilaitis, G. H. Altman, J. Chen, H. J. Jin, V. Karageorgiou and D. L. Kaplan, Macrophage responses to silk, Biomaterials 2003, 24: 3079–3085. 39. W. Zaoming, R. Codina, E. Fernandez-Caldas and R. F. Lockey, Partial characterization of the silk allergens in mulberry silk extract, J Allergy Clin Immunol 1996, 6: 237–241. 40. M. Dewair, X. Baur and K. Ziegler, Use of immunoblot technique for detection of human IgE and IgG antibodies to individual silk proteins, J Allergy Clin Immunol 1985, 76: 537–542. 41. S. Kurosaki, H. Otsuka, M. Kunitomo, M. Koyama, R. Pawankar and K. Matumoto, Fibroin allergy IgE mediated hypersensitivity to silk suture materials, J Nippon Med Sch 1999, 66: 41. 42. G. Ussia, D. Feldmann, M. Galletti, A. Salerno, A. Jacono and G. Galletti, Histopathological aspects of tissue reactivity to suture materials in microsurgical arterial, anastomosis, Ital J Surg Sci 1985, 15(3): 287–292. 43. A. Lendlein and R. Langer, Biodegradable, elastic shape-memory polymers for potential biomedical applications, Science 2002, 296: 1673–1676. 44. A. R. McKenzie, An experimental multiple barbed suture for the long flexor tendons of the palm and fingers, Preliminary report, J Bone Joint Surg (br) 1967, 49(3): 440–447. © Woodhead Publishing Limited, 2010
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Biodegradable textile yarns
S. M u k o p a d h y a y, Indian Institute of Technology, Delhi, India
Abstract : Biodegradable materials have the ability to break down, safely and relatively quickly, by biological means, into raw materials and disappear into the environment. Biodegradable polymers have gained wide acceptance due to their environmentally friendly nature and are classified according to their method of synthesis, chemical composition, processing methods and application. This chapter deals with fibres and yarns manufactured from biodegradable polymers using the conventional spinning techniques like melt and solution as well as modern spinning techniques like electrospinning. The chapter also covers yarns from mineral and other natural sources. Key words : biodegradable, biopolymers, PLA, spinning, fibres, yarns.
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Introduction: principles and importance of sustainable yarns
Human beings have used natural fibres and materials since ancient times. The advent of cheaper synthetic fibres and materials, with higher durability and higher quality consistency, led to preferences shifting towards synthetic materials. The durability of synthetic materials, i.e. their slow degradation characteristics, also proved to be their drawback. Serious problems with their disposal resulted in a real threat to the environment. While a small fraction of these products were incinerated, most of them finished up in landfills at the end of their useful life; both methods of disposal were expensive and posed serious ecological concerns. The importance of biodegradable materials was soon understood and well appreciated. Biodegradable generally implies hydrolysable at temperatures up to 50°C (e.g. in composting) over a period of several months to one year. Non-toxic degradation products are, of course, also important prerequisites for any potential application. Biodegradation of polymeric biomaterials involves cleavage of the hydrolytically or enzymatically sensitive bonds in the polymer, leading to polymer degradation. Polymeric biomaterials can be further classified into hydrolytically degradable polymers and enzymatically degradable polymers. It should be noted that most of the naturally occurring polymers undergo enzymatic degradation. Biopolymers are slowly becoming practicable substitutes for petroleumbased polymers. The building and construction industry, the automobile 534 © Woodhead Publishing Limited, 2010
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industry and the apparel sector have had encouraging results from the use of environmentally friendly biomaterials. Sustainable yarns use biomaterials or biodegradable polymers as starting materials and the yarns produced can be used in various sectors, especially in medical textiles.
16.1.1 Biodegradable polymers The past three decades have seen a major revival in interest for synthetic absorbable polymers. The requirement for absorbable polymers was driven by the need to replace highly tissue-reactive, absorbable, collagen-based sutures with synthetic polymers, which elicit a milder tissue response. This led to the early development of polyglycolide as an absorbable polyester suture. Many polymeric systems were investigated as candidates for absorbable implants and drug carriers. However, ester-based polymers emerged as the best candidates amongst clinically used systems and others that were under investigation. Biodegradable polymers are classified according to their method of synthesis, chemical composition, processing methods, application, etc. According to Clarinval and Halleux,1 such polymers can be divided into two types – those from natural origins and those from mineral origins. The sub-groups of the former include polysaccharides (e.g. starch, cellulose), proteins (e.g. casein, silk and wool), polyesters produced by microorganisms or plants (e.g. polyhydroxyl alcanoates, poly-3-hydroxybutyrate), and polyesters synthesized from bio-derived monomers (polylactic acid). There is another sub-class of biopolymers, derived from mineral origins, consisting of aliphatic polyesters (e.g. polyglycolic acid, polycaprolactone), aromatic polyesters (polybutylene succinate terephthalate) and polyvinyl alcohols. The majority of researchers are more interested in fibres with high breaking strength values, as it is well recognized that absorbable fibres suitable for constructing biomedical constructs, for example, as in certain surgical sutures and meshes as well as prosthetic tendons and ligaments, must be based on polymers that meet certain requirements. The polymers are expected to have: ∑ High molecular weight ∑ A high degree of crystallinity ∑ Minimum or no monomeric species. There are several exhaustive reviews on such biopolymers. The objective of this chapter is to discuss the fibres/yarns produced from these biopolymers and their applications. The subsequent sections discuss a few of the interesting developments in the use of such polymers as fibres/yarns.
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Fibres from biodegradable polymers of natural origins
16.2.1 Fibres based on chitosan and starch Fibres of chitosan and starch, using salicylic acid (SA) as a model drug incorporated in different concentrations, were obtained by Wang et al.2 They spun the solution through a viscose-type spinneret into a coagulating bath containing aqueous tripolyphosphate (TPP) and ethanol. Characterization of the chemical, morphological and mechanical properties was carried out, as well as studies of the factors that influence the release of the drug from the chitosan/starch fibres. These factors include the component ratio of chitosan and starch, the loaded amount of SA, the pH and the ionic strength of the release solution. The diameter of the fibres was around 15 ± 3 mm. The best values for the tensile strength, at 12.21 cN/tex, and breaking elongation, at 25.13%, of the blend fibres were obtained when the starch content was 30 wt%; the water-retention value (WRV) of blend fibres increased as the composition of starch was raised. The results of controlled release tests showed that the amount of SA released increased with an increase in the proportion of starch present in the fibre. Moreover, the release rate of the drug decreased as the amount of drug loaded in the fibre increased, but the cumulative release amount increased. The chitosan/starch fibres were also sensitive to pH and ionic strength. The release rate was accelerated by a lower pH and a higher ionic strength, respectively. All the results indicated that the chitosan/starch fibre is potentially useful for drug delivery systems. The effects of high-speed melt spinning and spin drawing on the structure and the resulting properties of bacterially generated poly(3-hydroxybutyrate) (PHB) fibres were investigated by Schmack et al.3 The fibres were characterized by their degree of crystallinity using differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS), by their orientation using WAXS, and by the textile’s physical properties. The WAXS studies revealed that the fibres spun at high speeds and high draw ratios possessed orthorhombic (a modification) and hexagonal (b modification) crystals, the latter as a result of stress-induced crystallization. The fibre structures formed during these processes were fibril-like, as shown by the atomic force microscopy images. The maximum physical break stress, the modulus, and the elongation at break observed in the fibril-like spin-drawn fibres were about 330 MPa, 7.7 GPa and 37%, respectively. The fibres obtained by a low draw ratio of 4.0 had spherulitic structures and the textile had poor physical properties.
16.2.2 Fibres from polylactic acid One of the most promising biodegradable polymers is polylactide (PLA), an aliphatic polyester. PLA is of great interest from the viewpoint of © Woodhead Publishing Limited, 2010
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environmental protection due to its mechanical properties profile, its thermoplastic processability, and its biodegradability. PLA has been used for implantable sutures for decades and researched as a promising candidate for tissue engineering scaffolds. Due to the chiral nature of lactic acid, several distinct forms of polylactide exist: poly-l-lactide (PLLA) is the result of polymerization of l,l-lactide. PLLA fibres have been thoroughly researched since the 1970s. Polymerization of a racemic mixture of l- and d-lactides usually leads to the synthesis of poly-dl-lactide (PDLLA). Initial investigations led to PLLA and PDLLA fibres, both with a tensile strength of 2.5 g/denier. Schneider obtained the above fibres with strength of 0.5–0.7 GPa.4 Eling et al.5 produced fibres with a tensile strength of 0.5 GPa and modulus of 7 GPa. Further improvement was achieved by Hyon et al.6, who achieved a strength of 0.7 GPa and a modulus close to 9 GPa. It has been shown by Schmack et al.7 that PLA type LA 0200 K, polymerized by means of reactive extrusion, can be spun both in a highspeed spinning process with a take-up velocity of up to 5000 m/min and in a spin drawing process up to a draw ratio of 6. The results showed that a degradable thermoplastic polymer could be produced in larger amounts by reactive extrusion polymerization of PLA. It was also shown that high-speed spinning achieved only average strength values while the spin-draw process resulted in better properties.
16.3
Spinning of PLA polymers
Experiments using the various general methods of fibre spinning, through melt, from solution, and by dry-jet wet spinning, have all been performed for PLA. The distinct features of each of these processes were subsequently reflected in the fibre properties. The thermoplastic nature of PLA allows melt spinning to be used, which is still the simplest process, with higher production speeds. Solution spinning is resorted to in cases where melt spinning is not possible, either because the polymer degrades while melting or the melt is thermally unstable. An excellent review by Gupta et al.8 summarizes all the methods of spinning polylactic acid fibres. Some of the interesting features of fibres spun using the various methods are discussed here.
16.3.1 Melt spinning method Melt spinning has been extensively used for the production of PLA fibres. A comparison of the different methods is shown in Table 16.1.9 In another study by Nishimura et al.,10 melt spinning and melt drawing of poly(l-lactic acid) (PLLA) were carried out with a melt spinning machine (Fig. 16.1), and the mechanical properties, structure and biodegradability
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Author (year) Initial Mv Extrusion (¥ 10–3) temperature (°C)
Collection speed (m min–1)
Nozzle diameter (mm)
As-spum fibre Final Mv crystallinity (¥ 10–3) (%)
Schneider (1972) 19 182 Eling et al. (1982) < 300 Hyon et al. (1984) 360 Dauner et al. (1992) 98 Penning et al. (1993) 280
? 0.25–0.35 ? ? 1
0.13–3.8 1 1 0.5 0.25
? < 114 25–500 ? 180–260 ? 5 110 150 ? 38 76 42 100 83
160–190 185 200 190 210
Drawn fibre diameter (µm)
Fibre strength/ modulus (GPa) 0.48–0.69/7 0.5/7 0.7/8.5 0.4/? 0.53/9
Mv = viscosity average molecular weight Source: yuan et al.9 Schneider A. K. Polylactide sutures, US Patent 3,636,956, 1972. B. Eling, S. Gogolewski and A. J. Pennings, ‘Biodegradable materials of poly(L-lactic acid): 1. Melt-spun and solution spun fibers’, Polymer, 23, 1982, 1587–93. S. H. Hyon, K. Jamshidi and Y. Ikada, in Polymeric biomaterials, edited by S. W. Shakby, A. S. Hoffman, B. D. Rather and T. A. Horbell, Plenum Press, New York, 1984, p. 5100. M. Dauner, E. Muller, B. Wagner and H. Planck, In vitro degradation of polylactides depending on different processes, in Degradation Phenomena On Polymeric Biomaterials edited by H. Planck, M. Dainer and M. Renardy, editors. Springer, Berlin, 1992. pp. 107–22. J. P. Penning, H. Dijikstra and A. J. Pennings ‘Preparation and characterization of absorbable fibers from L-lactide copolymers’, Polymer, 34,1993, 942–51.
Technical textile yarns
Table 16.1 Extrusion conditions and final properties of fibres produced by different authors
Biodegradable textile yarns 35 mm extruder 220°C
First roll
Water bath Cooling 45°C
Second roll
Water bath (2 m) Drawing 98°C
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Third roll
Water bath (3 m) Drawing 98°C
Winder
16.1 Outline of the production of melt spinning and drawing. Fibre axis
Crystal region Amorphous region
Degradation (hydrolysis)
Crack
16.2 Speculative structure and degradation mechanism for the PLLA.
of the PLLA fibre were investigated. PLLA fibre with a tensile strength of 0.81 GPa was successfully obtained from two stages of drawing at a draw ratio of 18 in hot water. This fibre had enough tensile strength for general engineering use. The fibre could be degraded under controlled composting conditions at 70°C for 1 week. SEM observations of the fibre revealed a regular pattern of cracks running in a vertical direction to the fibre axis. It was further observed that hydrolytic degradation also proceeded along with the vertical cracks, as explained in Fig. 16.2. The effect of viscosity average molecular weight on the properties of poly(llactic acid) (PLLA) fibres in conjunction with drawing was investigated by Yuan et al.11 using a two-step melt-spinning method (melt extrusion and hot draw) for the PLLA. They used three different viscosity-average molecular weights (494,600, 304,700 and 262,800). Before spinning, the polymer flakes were first milled into powders and dried in a vacuum. It was found that the viscosity-average molecular weight of PLLA dropped sharply by © Woodhead Publishing Limited, 2010
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13.1–19.5% during pulverization and by 39.0–69.0% during melt extrusion. Melt extrusion, according to the authors, should be carried out at a die temperature higher than 230°C for raw materials with a higher crystallinity, such as PLLA-a and PLLA-c, and higher than 220°C for PLLA-b, which has a lower crystallinity. The hot-draw process in this study had a small effect on the viscosityaverage molecular weight of PLLA. Smoother fibres were obtained with a die temperature of at least 230°C for raw materials with higher crystallinity (more than 75%) and at least 220°C for raw materials with lower crystallinity (about 60%). The tensile moduli of the as-spun PLLA fibres were in the range 1.2–2.4 GPa (Table 16.2), and these moduli were raised to 3.6–5.4 GPa (Table 16.3) after hot drawing. Tables 16.2 and 16.3 show that the tensile moduli tended to be higher when the original molecular weight was higher or when the extrusion temperature was lower. The ultimate strengths of the as-spun fibres were in the range 42–103 MPa. After hot drawing, the values rose dramatically to 300–600 MPa.
16.3.2 Dry spinning method Researchers have tried the dry spinning method, which results in better fibre properties. Gogoloewski and Pennings succeeded in getting fibres of strength 1.2GPa12 and Young’s modulus in the range 12–15 GPa by hotdrawing fibres close to their melting point, spun from a solution of PLLA in good solvents such as dichloromethane and trichloromethane (Fig. 16.3). The tensile strength of the fibres was strongly dependent on the molecular weight of the PLLA and on polymer concentrations in the spinning solution. Changing the polymer concentration in the spinning solution gave rise to the formation of fibres of different shapes and porosity. Fibres spun from 10–20% solutions at room temperature exhibited a regular structure due to melt fracture. The hot drawing of these materials at a temperature close to their melting point yielded fibres with a tensile strength up to 1.2 GPa and Young’s modulus up to 15 GPa. The tensile strength of the hot-drawn fibres increased with draw ratio and molecular weight. In Fig. 16.4, the broad endotherm, 1, is shown for the as-spun fibre. Endotherms 2, 3 and 4 were obtained for the fibres drawn at 200°C to different draw ratios. The tensile strength of these fibres is 0.1, 0.5, 0.8 and 1.2 GPa for 1, 2, 3 and 4, respectively. The broad melting endotherm of the as-spun fibre transforms into a high and narrow melting peak, seen for all the hot-drawn fibres, implying a higher perfection in crystal structure. Later, Leenslag and Pennings13 produced fibres with a strength of 2.3 GPa from solutions of PLLA in chloroform–toluene mixture. In another study by Postema et al.,14 variation in the temperature of the
© Woodhead Publishing Limited, 2010
Table 16.2 Tensile properties of as-spun PLLA fibres Die temperature (°C)
Diameter (µm)
Tensile modulus (GPa)
Ultimate strength (MPa)
Ultimate Yield Elongation (%) strength (MPa)
Strain at yield (%)
PLLA-a
220 230 240
319 ± 19 290 ± 18 319 ± 21
2.15 ± 0.22 2.32 ± 0.15 1.76 ± 0.56
95.4 ± 7.9 79.3 ± 8.5 60.9 ± 17.1
395 ± 40 435 ± 54 4.19 ± 0.45
68.5 ± 4.5 67.9 ± 3.5 –*
3.52 ± 0.55 3.32 ± 0.66 –*
PLLA-b
210 220 230
340 ± 23 298 ± 40 310 ± 6
2.04 ± 0.15 2.24 ± 0.24 2.02 ± 0.26
60.7 ± 2.3 71.9 ± 9.3 66.0 ± 7.0
293 ± 85 440 ± 54 105 ± 163
62.9 ± 3.6 62.5 ± 5.8 69.5 ± 3.3
3.65 ± 0.57 3.60 ± 0.99 3.96 ± 0.17
PLLA-c
210 220 230
339 ± 36 269 ± 22 335 ± 13
1.81 ± 0.29 2.15 ± 0.18 2.19 ± 0.08
50.6 ± 4.9 50.8 ± 8.5 53.2 ± 11.2
8.96 ± 4.43 74.8 ± 91.5 33.4 ± 39.6
55.7 ± 5.0 58.3 ± 7.1 61.2 ± 5.9
3.90 ± 0.39 3.59 ± 0.68 2.96 ± 0.44
*Samples of a240 broke before or near the yield point. Source: yuan et al.9
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Sample
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Sample
Die temperature (°C)
Diameter (µm)
Draw ratio
Tensile modulus (GPa)
Ultimate Ultimate Yield Strain strength (MPa) Elongation (%) strength (MPa) at yield (%)
PLLA-a
220* 230 240
147 ± 7 151 ± 9 146 ± 11
4.71 4.75 4.77
5.22 ± 0.24 4.74 ± 0.25 4.58 ± 0.14
535 ± 70 488 ± 57 412 ± 27
39.2 ± 3.3 55.6 ± 7.7 65.4 ± 9.3
–† 148 ± 7 127 ± 7
–† 3.98 ± 0.24 3.07 ± 0.16
PLLA-b
210* 220 230
145 ± 10 138 ± 13 134 ± 8
5.50 4.66 5.35
4.96 ± 0.43 4.47 ± 0.31 3.88 ± 0.27
484 ± 86 480 ± 84 332 ± 34
40.8 ± 6.6 51.3 ± 7.2 57.8 ± 7.9
–† 139 ± 13 116 ± 3
–† 4.00 ± 0.61 3.65 ± 0.43
PLLA-c
210 220 230
149 ± 10 119 ± 9 138 ± 8
5.18 5.11 5.89
4.46 ± 0.11 4.12 ± 0.36 4.43 ± 0.53
365 ± 40 400 ± 55 415 ± 50
66.8 ± 10.3 73.6 ± 13.1 67.3 ± 7.8
117 ± 4 112 ± 10 121 ± 11
3.12 ± 0.29 2.96 ± 0.15 3.23 ± 0.37
*Samples of a220hd and b210hd were tested in the Instron tester. †Samples of a220hd and b210hd showed no significant yield points.
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Table 16.3 Tensile properties of hot-drawn PLLA fibres
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B
A
16.3 Extruder for dry spinning of fibres: A general view; B motor drive; C collecting drum; D glass cylinder with capillary die of 1 ¥ 25 mm; E cylinder holder.
E
D
C
Endotherms
1
2
3 4
120
140
160 T(°C)
180
200
16.4 Melting endotherms of PLLA fibres: 1 as-spun fibre; 2, 3 and 4 fibres drawn at 200°C to l = 10, 16 and 20, respectively (after Gogoloewski and Pennings12).
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surroundings of the spin line during dry spinning of PLLA solutions led to ultimate tensile strengths after hot drawing that varied between 1.1 and 2.2 GPa. Phase separation followed by rapid crystallization, preserving the entanglement network, led to large extrudate swells and heterogeneous filaments, which had poorer tensile properties after hot drawing. Minimum extrudate swell was achieved by suppressing the phase separation and crystallization so that slippage of chains led to homogeneous filaments, which could be hot-drawn to filaments with a tensile strength of 2.2 GPa.
16.3.3 Poly(hydroxybutyrate) fibre One of the more interesting biodegradable polymers is poly(3-hydroxybutyrate) (PHB), an aliphatic polyester that can be produced by many types of microorganisms in order to store carbon as an intracellular energy source. Because of its bacterial origin, PHB can be obtained in exceptionally pure form without any inclusion of catalyst residues and as a stereoregular optically active isotactic polyester. Many studies have reported on the identification of the crystal structure,15 crystallization,16 thermal behaviour, and chemical composition17 of PHB. In a study by Schmack et al.,18 the effects of high-speed melt spinning and spin drawing on the structure and resulting properties of bacterially generated poly(3-hydroxybutyrate) (PHB) fibres were investigated. The fibres were characterized by their degree of crystallinity using differential scanning calorimetry and wide-angle X-ray scattering, which revealed that the fibres spun at high speeds and high draw ratios possessed orthorhombic (a modification) and hexagonal (b modification) crystals. Atomic force microscopy images showed that fibre structures formed during these processes were fibril-like. The maximum physical break stress, the modulus and the elongation at break observed in the fibril-like spin-drawn fibres were about 330 MPa, 7.7 GPa and 37%, respectively. Load–elongation curves of PHB fibres showed that their mechanical properties were strongly dependent on the draw ratios, which determined the chain extension and the molecular orientation along the fibre axis. Figure 16.5 shows that a marked difference exists between the curves of the fibres produced by draw ratios of 4.0 and 4.5. The fibres produced with a draw ratio of 4.0 were brittle and had no significant elongation at break and tensile strength. Iwata et al.19 obtained fibres of biodegradable poly((R)-3-hydroxybutyrate) homopolymer with high tensile strength that were processed from a ultrahigh molecular weight polymer by a method combining cold-drawing and two-step-drawing procedures. The melt-spun fibre quenched into ice water (amorphous preform) was easily and reproducibly stretched at a temperature below the glass transition temperature of 4°C. The oriented amorphous fibre was further stretched at room temperature and then annealed to fix the
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DR = 5.4
200 Tension (MPa)
T = 40/60°C T = 45/60°C
DR = 5.9
250
545
DR = 5.5
150
DR = 5.0 DR = 5.4
100
DR = 4.5 50
DR = 4.0
0 0
20
40 60 Elongation (%)
80
100
16.5 Variation of mechanical properties with draw ratio, DR (after Schmack et al.18).
extended polymer chains. The cold- and two-step-drawn fibre demonstrated a tensile strength of 1.32 GPa, elongation to break of 35%, and Young’s modulus of 18.1 GPa, and could be used for fishing lines or sutures. The molecular and higher-ordered structures of P(3HB) fibres were analysed by micro-beam X-ray diffraction (beam size 0.5 mm) using the Fresnel Zone Plate technique with synchrotron radiation at SPring-8, Japan, and it revealed that the P(3HB) fibre had a new core sheath structure with mainly a 21 helix conformation in the sheath region and mainly a planar zigzag conformation in the core region.
16.3.4 Poly (p-dioxanone) fibres Poly(p-dioxanone) (PPDX or PPDO) is a synthetic poly(ester–ether) that is of interest for biomedical applications due to its biodegradability, biocompatibility, bioabsorbability and softness. It was patented in 1977 as an absorbable polymer and processed for use as a monofilament surgical suture in the early 1980s. In a study by Park et al.,20 biodegradable poly(p-dioxanone) (PPDO) fibre was used as reinforcement in a PLLA matrix for orthopaedic implant materials. The tensile strength of PPDO fibre with hydrolysis time and plasma treatment time was measured by a single fibre tensile test. The PPDO fibre was fixed on an acryl frame using Kapton tape, and hydrolysed in deionized
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water. In order to accelerate the degradation, the temperature was raised to 70°C in a clean oven. The range of the degradation time was the initial state, 3 and 5 days, respectively. Plasma treatment time was consequently changed from the initial state to 600 s. As the hydrolysis time elapsed, both the tensile strength and modulus of the PPDO fibre decreased sharply (Fig. 16.6). After 3 and 5 days, its tensile strength reduced to almost a half and a tenth, respectively, compared with the initial state. This could be explained by the fact that as the polymeric chain length or molecular weight decreased gradually, surface cracks could be induced (Fig. 16.7) by hydrolytic degradation. The tensile strength of 600
3.0
90
2.5
75
400
2.0
60
300
1.5
200
1.0
30
100
0.5
15
0
0
0
Elongation
0
3 Hydrolysis time (days)
5
45
Elongation (%)
Strength (MPa)
500
Modulus (GPa)
Strength Modulus
16.6 Mechanical properties of PPDO fibre with elapsing hydrolysis time (after Park et al.20).
(a)
(b)
16.7 SEM photographs of PPDO fibre (a) at the initial state, (b) after 5 days (after Park et al.20, reproduced with permission).
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conventional fibre is known to be strongly dependent upon surface or internal flaws. Figure 16.8 shows the typical microfailure modes of PPDO fibre (a) at the initial state, (b) after 3 days and (c) after 5 days. The number of fragments increased and the breakage pattern varied with changing hydrolysis time. In the initial state, PPDO fibre showed ductile microfailure modes such as ‘plastic deformation, and diagonal and internal fractures’. After 5 days, the failure was due to vertical fractures as a result of the increased brittleness of the fibre, as explained by the authors. Since the tensile strength of PPDO fibre at the initial state was higher than that after hydrolysis, the stress-whitening distribution induced by PPDO fibre fracture was larger and clearer. As hydrolysis progressed, the stress-whitening state of the PPDO fibre decreased gradually.
100 mm
100 mm (a)
100 mm
100 mm (b)
100 mm
100 mm (c)
16.8 Microfailure modes of PPDO fiber with hydrolysis time (a) at the initial state, (b) after 3 days, and (c) after 5 days (after Park et al.20, reproduced with permission).
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16.4
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Electrospinning
Biodegradable fibres have mostly been prepared from polymer solution or melt. The diameters of fibres made by conventional methods (melt, dry and wet spinning) are in the range 5–500 mm. In the past few years, electrospinning has been developing rapidly because it can produce a diameter 100 times smaller than that of conventional fibres. Electrospinning is a unique method that produces polymer fibres with a diameter ranging from the nano level to a few microns using an electrically driven jet of polymer solution or melt. The morphology of electrospun fibres depends on various parameters such as (i) solution parameters including viscosity, conductivity and surface tension, (ii) controlled variables including hydrostatic pressure in the capillary, electric potential at the tip and the tip-to-collector distance (TCD), (iii) ambient parameters including temperature, humidity and air velocity in the electrospinning chamber, etc. The importance of solution properties in biodegradable poly(e-caprolactone) (PCL) materials was demonstrated by Lee et al. 21 Nano-structured PCL filaments and subsequently non-woven mats were prepared by the electrospinning process. In this study, three types of solution were used. One sample was dissolved in only methylene chloride (MC), the second was dissolved in a mixture of MC and N,N-dimethylformamide (DMF), and the third was dissolved in a mixture of MC and toluene. MC, toluene and DMF are a good, poor and non-solvent for PCL, respectively. Using MC only, the electrospun fibres (Fig. 16.9) had very regular diameter of about 5500 nm, but electrospinning was not made easier. For the mixture of MC and DMF, electrospinning was definitely enhanced and the fibre diameter Electrode
Capillary tube
Collector
(+) charge Power supply
Ground
16.9 Experimental set-up device for electrospinning process (after Lee et al.21).
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also decreased dramatically with increasing DMF volume fraction. This was due to the high electrical properties of the solution such as its dielectric constant and conductivity. However, with an increasing toluene volume fraction, electrospinning was greatly restricted due to its very high viscosity and low conductivity. As a result, it was observed that solution properties are some of the most important parameters in electrospinning.
16.4.1 Aligned nano-PLLA fibres Both aligned and random PLLA fibres (Fig. 16.10) were fabricated by the electrospinning technique under optimum conditions by Yang et al.22 The polymer solution was prepared by dissolving the PLLA (Mw = 300,000, Polysciences, USA) into dichloromethane (DCM)/n,n-dimethylformamide (DMF) (70:30) at concentrations of 1%, 2%, 3% and 5% w/w. The distance between the syringe needle tip and the collector was adjusted to 10 cm. A rotating disc was used for collecting aligned fibres, whereas a flat aluminium plate was used for collecting random fibres.
(a)
(b)
(c)
(d)
16.10 SEM micrographs of PLLA: (a) aligned nanofibres; (b) aligned microfibres; (c) random nanofibres; (d) random microfibres (after Yang et al.22).
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16.4.2 Electrospinning of PDLA/PLLA Electrospinning technology is well suited to processing natural biomaterials and synthetic biocompatible or bioabsorbable polymers for biomedical applications. Potential applications of these non-woven nanostructured membranes include filtration, anti-adhesion membranes, wound dressing scaffolds, and artificial blood vessels. Zong et al.23 have investigated the effects of varying the processing parameters in electrospinning on the microstructure of biodegradable amorphous poly(d,l-lactide) (PDLA) and semi-crystalline poly(l-lactide) (PLLA) membranes. The results confirmed that the morphology of electrospun polymer fibres is a function of the strength of the electric field, the solution viscosity (e.g. concentration), the charge density of the solution (by salt addition), and the solution feeding rate. It was shown that a higher concentration and higher charge density of the solution favoured the formation of uniform nanofibres with no bead-like textures. The diameter of the nanofibres increased with the electrospinning voltage as well as the feeding rate of the solution. The effect of salt on the structure and morphology of the electrospun PDLA fibres is important since most drugs form charged ions in water. The addition of a small amount of salt or antibiotic drugs was found to greatly change the morphology of electrospun PDLA fibres from a beads-on-fibre structure to a uniform fibre structure. The electrospinning of crystallizable PLLA resulted in a decrease in the glass transition and crystallization temperatures, but an increase in the crystallization rate. Electrospinning was found to significantly retard the crystallization of PLLA. The amorphous phase in the nascent electrospun PLLA membrane was probably not a pure amorphous phase. Some metastable states, such as oriented chains with no helical structures, may exist between the amorphous and crystalline states of electrospun PLLA fibres.
16.4.3 PLLA yarns in scaffolds Various scaffolds were designed for ligament tissue engineering by Ge et al.24 Knitted scaffolds of poly-l-lactic acid (PLLA) yarns and co-polymeric yarns of PLLA and poly(glycolic acid) (PLGA) were characterized and immersed in a medium for 20 weeks, before mass loss, molecular weight and pH value change in the medium were tested; changes in the mechanical properties were evaluated at different time points. Results showed that the knitted scaffolds had 44% porosity. There was no significant pH value change during degradation, while there was an obvious initial mass loss at 4 weeks, as well as a smooth molecular weight decrease of the PLLA. PLGA degraded more quickly, while PLLA kept its integrity for at least 20 weeks. The Young’s modulus increased while tensile strength and strain at break decreased with degradation time; however, they all maintained the basic requirements for
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ACL reconstruction. This showed that knitted polymeric structures could serve as potential scaffolds for tissue-engineered ligaments.
16.5
Fibres from biodegradable polymers from mineral origins
16.5.1 PGA-co-PLA (PLGA) fibres Poly(lactic-co-glycolic acid), abbreviated as PLGA, is synthesized by means of random ring-opening co-polymerization of two different monomers, the cyclic dimers (1,4-dioxane-2,5-diones) of glycolic acid and lactic acid. PLGAs are amorphous and show a glass transition temperature in the range 40–60°C and degrade by hydrolysis of their ester linkages in the presence of water. Fu et al.25 studied the structure and properties of a bioabsorbable poly(glycolide-co-lactide) (PGA-co-PLA) fibre during several processing stages and the final in vitro degradation stage by means of wide-angle X-ray diffraction, dynamic mechanical analysis and mechanical property tests. In the orientation stage, an increase in the temperature of the first orientation roll encountered resulted in a lower level of crystallinity and larger crystallites. The temperature of the second pre-annealing roll (PR) encountered caused a smaller effect on the structure. In the hot-stretching stage after fibres were braided, the maximum crystallinity was achieved at around 126°C. Higher hot-stretching temperatures increased the crystal size, glass transition temperature (Tg) and tensile strength, but decreased the elongation at break and heat shrinkage near Tg. In the post-annealing stage, it was found that crystallinity, Tg and tensile strength all increased significantly while the heat shrinkage near Tg sharply decreased after annealing. This suggests that the internal stress accumulated in the orientation and hot-stretching stages could be effectively reduced by post-annealing. During in vitro degradation, crystallinity was found to increase with time while the heat shrinkage near Tg and in the supercooling region (Tg < T < Tm) was greatly reduced. These results support the process of cleavage-induced crystallization. Deng et al.26 studied the in vitro degradation behaviour of a poly(glycolideco-l-lactide) 90/10 monofilament in phosphate buffer solution at pH 7.4 over a temperature range of 27.5–47.5°C. The researchers found that the polymer monofilament gradually lost its tensile strength and molecular weight with increasing in vitro time. The hydrolytic degradation of the monofilaments followed a first-order behaviour. Higher temperatures accelerated the degradation process significantly. It was found that for a given tensile breaking strength retention (BSR), the dependence of degradation time on temperature could be illustrated by an Arrhenius-type equation, from which the activation energy was derived. Further analysis indicated that there were well-defined relationships between molecular weight and tensile strength,
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which could be illustrated mathematically. Finally, microscopic evaluation of the monofilament samples revealed visible changes in morphology on the surface and cross-section areas during the degradation process. The results from atomic force microscopy showed that the surface roughness of the monofilament tended to increase with in vitro time. Monofilament samples were examined by optical microscopy (OM) immediately following their removal from the in vitro bath. The representative OM images are presented in Fig. 16.11. These images show that the monofilament sample lost its transparency with increasing in vitro time, which is attributed by the authors to (i) recrystallization as a result of hydrolysis, (ii) crazing and cracking within the filament, and (iii) water diffusion into the material. SEM (Fig. 16.12) clearly shows the cracking formed at the later stage of degradation. An isolated longitudinal crack can be observed on the filament surface of the samples. The images of the cross-section of the monofilament indicate that a crack might have formed and propagated along the transition area between the skin and core of the monofilament. Deng et al.27 studied the effects of load and temperature on the in vitro degradation behaviour of poly(glycolide-co-l-lactide) 90/10 multifilament braids in phosphate buffer solution at pH 7.4. The property changes of the braids with time were monitored by tensile testing, gel permeation chromatography analysis, and scanning electron microscopy. The interrelationships between material properties, time and experimental conditions were explored. The results showed that the polymer braids gradually lost their strength and molecular weight with increasing in vitro time (Fig. 16.13). While the load levels applied had no effect on the materials, raising the temperature significantly accelerated the degradation. It was found that for a given tensile breaking strength retention (BSR), the dependence of degradation time on temperature could be illustrated by an Arrhenius-type equation. For all of
Day 0
Day 7
Day 12
Day 16
16.11 Morphological changes as revealed by optical microscopy.
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Day 7
Day 12
Day 16
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16.12 SEM results of monofilament (original magnification 350×).
16.13 Change of surface morphology with in vitro time (after Deng et al.27).
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the in vitro conditions investigated, the surface of the braided polymer, as well as the individual filaments comprising the braid, showed little change in appearance after SEM examination up to 500¥ magnification until after approximately a 50% drop in breaking strength was reached. Erosion or material loss could then be clearly seen on fibre surfaces.
16.5.2 Polyvinyl alcohol (PVA) fibres Polyvinyl alcohol (PVA) is an atactic material but it exhibits crystallinity as the hydroxyl groups are small enough to fit into the lattice without disrupting it. In 1958, Kuraray of Japan commenced the manufacture and sale of poval, a polyvinyl alcohol (PVA) resin used in the production of vinylon. In the ensuing years, the company continued to build on the excellence of that technology to expand its presence in global markets. Since 1983, rising concerns about the dangers of asbestos inhalation have brought PVA fibres into the limelight as an asbestos replacement. The current generation of PVA fibres, Kuralon K-II™, was introduced in 1998 and found success in a variety of applications, including earthquake-resistant curtain wall sidings for skyscrapers. By 2001, Kuraray was shipping out about 20,000 tons of PVA fibre globally for use in a wide range of cement applications. In the autumn of 2003, Kuralon K-II™ structural fibres for concrete and mortar were released for distribution in the North American market after achieving considerable success in Asia and Europe. There have been several studies on PVA fibres and their modification with single-walled nanotubes for use as reinforcements in composites and cement-based products, and the results of some interesting developments are discussed below. Zhang et al.28 worked on improving the strength of PVA fibres by gelspinning them with single-wall carbon nanotubes (SWNT). A homogeneous mixture of nanotubes, polyvinyl alcohol (PVA), dimethyl sulfoxide (DMSO) and water was prepared by stirring and sonication. The dispersion was extruded into the fibre via gel spinning. The modulus of the PVA/SWNT (3 wt%) composite fibre was reported by the authors to be 40% higher than that of the control PVA gel-spun fibre (Fig. 16.14). It was found that the SWNTs were well dispersed with DMSO as the solvent. Miaudet et al.29 investigated the resistivity of composite nanotube fibres made of polyvinyl alcohol and multiwalled carbon nanotubes. The authors found new applications for the fibres in conductive and multifunctional textiles or composites. The properties observed were justified by the authors as a result of the existence of amorphous regions in the basic polymer and the change in the amorphous fraction with annealing: ∑
When the fibres contained a large fraction of amorphous polymer, a substantial decrease in resistivity was observed in the vicinity of the © Woodhead Publishing Limited, 2010
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1.2
Tensile stress (GPa)
1 0.8
b
0.6 a 0.4 0.2 0 0
1
2
3
4 5 Strain (%)
6
7
8
9
16.14 Stress–strain curves of (a) PVA and (b) PVA/SWNT gel-spun fibres (after Zhang et al.28).
glass transition temperature (Tg) of the pure PVA. On the basis of X-ray diffraction characterizations, this behaviour was shown to result from the relaxation of stress in the polymer–nanotube composite. Slight structural modifications and partial loss of nanotube alignment at Tg could produce an increase in the density of intertube contacts and thereby a decrease in the electrical resistivity. ∑ Annealing the fibres at a high temperature reduced the fraction of amorphous PVA which became more crystalline. As a result, the conductivity became more stable and did not exhibit any abrupt variation at Tg. Instead, the conductivity was non-metallic with an effective semiconductor-type behaviour, as observed in other nanotube composites or even in pure nanotube assemblies. Fei and Gu30 manufactured thermo-crosslinking hydrogel fibres composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA). The hydrogel fibre was prepared by extruding the spinning dope from in situ polymerization of acrylic acid in the presence of PVA into a coagulating bath of saturated ammonium sulfate aqueous solution. The network was formed by thermally heating the dried fibres in a vacuum. The final hydrogel fibres exhibited pH-sensitive behaviour and showed a hysteresis loop in the pH range 2.5 to 12.5. The pH value at which the swelling ratio of the fibre had a jump in value shifted to a lower value with an increase of the PAA content within the network. With an increase in the heating temperature and time for the fibres, the swelling ratio decreased and the jump point pH shifted to higher pH value. The oscillatory swelling/contracting behaviour of the hydrogel fibre exhibited an easily reversible pH-responsive property.
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Jiang et al.31 used in situ microencapsulation to prepare a thermo-regulating fibre. The in situ microencapsulation of paraffin in PVA (fibre matrix) was performed by treating the as-spun fibre to promote the hydrolysis and polycondensation of ethyl orthosilicate (TEOS) at the interface between the paraffin and PVA matrix. The mechanism of hydrolysis and polycondensation of TEOS was studied by a simulation experiment. The authors found that the paraffin phases, tightly wrapped by TEOS hydrolysates, were present in the PVA matrix when the as-spun fibres were treated in an acidic condition. The thermo-regulating PVA fibre prepared by this method had a relatively high latent heat value (23.7 J g−1) and good latent heat stability. A study by Jiang et al.31 resulted in a new method which was called ‘in situ microencapsulation’. In this method, phase change materials (PCM) and membrane-forming reagents were added into polymer melts or solutions to form lacteal spinning dopes, which were spun via conventional spinning techniques to form as-spun fibres. Unlike the microencapsulated PCM composition spinning method, it was not necessary to add fixed-shape PCM microcapsules into the spinning fluids before spinning. The PCM microcapsules in the fibre matrix were formed by a post-treatment, i.e. treating the as-spun fibres under suitable conditions. Zhang et al.32 developed PVA short-fibre-reinforced fly-ash geopolymer composites (SFRGC), manufactured using extrusion. The effects of the fly-ash content and fibre volume fraction on the rheological and impact behaviours of SFRGC were systemically investigated. Freeze–thaw cycles and sulfuric acid attack tests were employed to study the durability of SFRGC. The authors demonstrated that for normally cured SFRGC, the addition of PVA fibre increased the ductility, especially with a high volume fraction of fibre, resulting in a change in the impact failure mode from a brittle pattern to a ductile one. As a result, a great increase in impact toughness is seen in SFRGC with a high fibre content. The long-term durability of PVA (polyvinyl alcohol) fibres used as reinforcement in cement-based products was assessed by Akers et al.33 after exposure of the products to natural weathering and an accelerated ageing process. The PVA fibres were extracted, then characterized by X-ray diffraction techniques. The mechanical properties of the extracted fibres were compared with the mechanical properties of the composite. In general, an increase in composite strength and stiffness was evident; this may, in part, have been associated with carbonation of the matrix and an increase in the PVA fibre-matrix interfacial bond. X-ray diffraction studies on the extracted PVA fibres indicated, in some cases, a loss of crystalline order with age (natural weathering), related to a disordering of the hydrogenbonded sheets. The possible changes were minor and had no influence on the tensile properties of the PVA fibres or the ageing properties of the composites. It was suggested that the PVA fibres that were part of the
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reinforcement of the cement matrix were durable over a period of at least 7 years.
16.5.3 Other fibres from natural sources Several fibres from natural sources have been used as biodegradable materials. Some of the interesting research on various fibres from natural sources is reported here. Several natural fibres/yarns have been used in high-end applications. Lignocellulosic fibres, especially, have been used as reinforcements, as summarized by Satyanarayana et al.,34 and used by Alvarez and his group35,36 and several others with biodegradable matrices. Alginate fibres Alginate fibres are generally prepared37,38 by injecting a solution of watersoluble alginate (usually sodium alginate) into a bath containing an acidic solution and/or a calcium salt solution to produce the corresponding alginic acid and/or calcium alginate fibres, respectively, which can be used to produce yarns and fabrics for medical applications. In one of the studies by Knill et al.,39 alginate fibres were modified by chitosan for potential use as wound dressings. Unhydrolysed and hydrolysed chitosans were utilized for the modification of sodium alginate/alginic acid fibres and the levels of chitosan incorporated onto/into the base alginate fibres were estimated by elemental analysis. The tensile properties (% elongation and tenacity) of the resultant chitosan/alginate fibres were determined in order to assess their potential suitability for application as wound dressings. Modification of the fibres with unhydrolysed chitosans generally resulted in a significant reduction in tenacity (and a reduction in % elongation if a water washing stage was not used), i.e. no increase in fibre strength was observed, implying that the unhydrolysed chitosan was more like a coating rather than something that penetrated or reinforced the alginate fibre (Fig. 16.15). It was observed that a reduction in the chitosan’s molecular weight had a positive effect on its ability to penetrate the alginate fibres, not only increasing the fibre’s chitosan content, but also reinforcing the fibre structure and thus enhancing its tensile properties. Hydrolysed chitosan/alginate fibres demonstrated an antibacterial effect and had the ability to provide a slow release/leaching of antibacterially active components. Fan et al.40 explored antibacterial fibres from alginate–carboxymethyl chitosan blend fibres. The fibres were prepared by spinning the mixture through a viscose-type spinneret into a coagulating bath containing aqueous CaCl2. The analyses indicated a good miscibility between the alginate and carboxymethyl chitosan, because of the strong interaction of intermolecular
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Technical textile yarns Sodium alginatal alginic acid core fibre Hydrolysed chitosan enterior
Hydrolysed chitosan enterior
Hydrolysed chitosan diffusion into core
16.15 Representation of an alginate/chitosan fibre showing the absorption of chitosan onto/into the base alginate fibre (after Knill et al.39).
hydrogen bonds. The best values of dry tensile strength and breaking elongation were obtained when the carboxymethyl chitosan content was 30 and 10 wt%, respectively. The wet tensile strength and breaking elongation decreased with an increase of carboxymethyl chitosan content. Antibacterial fibres, obtained by treating the fibres with an aqueous solution of N-(2-hydroxy)propyl-3-trimethylammonium chitosan chloride and silver nitrate, respectively, exhibited good antibacterial activity to Staphylococcus aureus. Pineapple fibres Pineapple fibres are generally extracted from the leaves of a pineapple plant. In a study by Luo and Netravali,41 the physical and tensile properties of pineapple fibres were characterized. Their tensile properties, like most natural fibres, showed a large variation. The average interfacial shear strength between the pineapple fibre and poly(hydroxybutyrate-co-valerate) (PHBV) was 8.23 MPa, measured using the microbond technique. Scanning electron microscopy (SEM) photomicrographs of the microbond specimens revealed an adhesive failure of the interface. Fully degradable and environmentally friendly ‘green’ composites were prepared by combining pineapple fibres and PHBV with 20 and 30% weight content of fibres placed in a 0±/90±/0± fibre arrangement. Although the tensile and flexural strength and moduli of these ‘green’ composites were lower than those of some wood specimens tested in the direction of the grain, they were significantly higher than those of wood specimens tested perpendicular to the direction of the grain. Abaca fibres Poly(3-hydroxybutyrate-co-3-hydroxyvaerlate) (PHBV) composites, reinforced with short abaca fibres (popularly known as manila hemp), were prepared
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by melt mixing and subsequent injection moulding. An investigation of their mechanical properties by Shibata et al.42 and a comparison with PHBV composites reinforced with glass fibre (GF) showed that the flexural properties of the PHBV/abaca composite were improved by surface treatment of the abaca with butyric anhydride and pyridine for 5 h because of an increase in interfacial adhesiveness between the matrix polyester and the surface-esterified fibre. This was obvious from the SEM micrographs. The flexural and tensile properties of the PHBV/treated abaca composite were comparable to those of the PHBV/GF composite, except for the tensile modulus, compared using the same weight fraction of fibre. The effects of lysine-based diisocyanate (LDI) as a coupling agent on the properties of biocomposites of poly(lactic acid) (PLA), poly(butylene succinate) (PBS) and bamboo fibre (BF) were investigated by Lee and Wang.43 The tensile properties, water resistance and interfacial adhesion of both the PLA/BF and PBS/BF composites were improved by the addition of LDI, whereas thermal flow became somewhat difficult due to crosslinking between the polymer matrix and BF. Crystallization temperature and enthalpy in the two composites increased and decreased with increasing LDI content, respectively. The heat of fusion in both composites was reduced by the addition of LDI, whereas there was no significant change in melting temperature. The thermal degradation temperature of both composites was lower than that of the pure polymer matrix, but the composites with LDI showed a higher degradation temperature than those without LDI. The enzymatic biodegradability of PLA/BF and PBS/BF composites was investigated using proteinase K and lipase PS, respectively. Both composites could be quickly decomposed by the enzymes but the addition of LDI delayed the degradation. Silk yarns In research by Horan et al.,44 B. mori silk yarns were used as a model system to demonstrate the potential benefits and drawbacks of several textile methods used to fabricate tissue engineering scaffolds. Fibres were plied, twisted, cabled, braided and/or textured (Fig. 16.16) to form several geometries with a wide range of mechanical outcomes. Braids, one of the most commonly used textile structures, were found to be limited by a change in stiffness following the locking angle and, therefore, potentially not the ideal structure for tissue engineering. Cabled yarns appeared to be most flexible in mechanical outcomes with a highly organized geometry. Twisted yarns, while more economical than cabled yarns, showed a higher stiffness and a lower percentage elongation at break than cabled yarns.
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16.16 DSC scans of as-received: (a) PLLA yarns; (b) yarns ex-derived fabrics.
16.6
Applications of biodegradable fibres/yarns
A biodegradable hybrid scaffold was prepared from fibrin and poly(glycolic acid) (PGA) fibre by Hokugo et al.45 Mixed fibrinogen and thrombin solution, homogeneously dispersed in the presence of various amounts (0, 1.5, 3.0 and 6.0 mg) of PGA fibre, was freeze-dried to obtain fibrin sponges, with or without the incorporation of PGA fibre. Using scanning electron microscopy, the fibrin sponges were observed to have an interconnected pore structure, irrespective of the amount of PGA fibre incorporated. PGA fibre incorporation enabled the fibrin sponges to significantly enhance their compression strength.
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Analysis showed that a fibrin sponge reinforced by fibre incorporation is a promising three-dimensional scaffold of cells for tissue engineering. Wood flour was converted into thermoplastics by Zhang et al.46 through complete benzylation treatment, which introduces large benzyl groups onto cellulose and partially deteriorates the ordered structure of the crystalline regions. By changing a series of parameters, such as the reaction temperature, concentration of aqueous caustic solution, species of phase transfer catalyst, etc., the extent of benzyl substitution was regulated within a wide range so that a balanced thermal formability and mechanical performance of the modified wood flour were obtained. By using plasticized China fir sawdust as the matrix, both discontinuous and continuous sisal fibres were compounded to produce composites from renewable resources. These all-plant fibre composites were characterized by moderate mechanical properties and full biodegradability. Schakenraad et al.47 manufactured biodegradable hollow fibres of polyl-lactic acid (PLLA) filled with a suspension of the contraceptive hormone levonorgestrel in castor oil which were implanted subcutaneously in rats to study the rate of drug release, rate of biodegradation and tissue reaction caused by the implant. The in vivo drug release was compared with the release in vitro using different release media. Fibres disinfected with alcohol showed a zero-order release, both in vitro and in vivo, for over 6 months. The influence of plant fibres, such as flax, jute, ramie, oil palm fibres and fibres made from regenerated cellulose, on the mechanical properties of biodegradable polymers was investigated by Wollerdorfer and Bader 48 using thermoplasts like polyesters, polysaccharides and blends of thermoplastic starch. The composites were produced by extrusion compounding with a co-rotating twin-screw extruder. The pellets obtained were further processed into tensile test bars by injection moulding. The chemical similarity of polysaccharides and plant fibres, which consist mainly of cellulose, resulted in an increased tensile strength of the reinforced polymers. For reinforced thermoplastic wheat starch, it was four times better (37 N/mm2) than without fibres. The reinforcement of cellulose diacetate and starch blends caused a stress increase of 52% (55 N/mm2) and 64% (25 N/mm2), respectively. The mechanical properties of an environmentally friendly composite made of kenaf fibre and polylactic acid resin were investigated by Nishino et al.49 The Young’s modulus (6.3 GPa) and the tensile strength (62 MPa) of the kenaf/PLLA composite (fibre content = 70 vol%) were comparable to those of traditional composites. These properties were higher than those of the kenaf sheet and the PLLA film individually. The authors attributed the results to a strong interaction between the kenaf fibre and PLLA. In addition, the storage modulus of the composite remained unchanged up to the melting point of PLLA. The effects of the molecular weight of PLLA and the orientation of the
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kenaf fibres in the sheet on the mechanical properties of the composite were also investigated. It was found that kenaf fibre can be a good reinforcement of high-performance biodegradable polymer composites. In a study by Plackett et al.,50 a commercial polylactide was converted to a film and then used in combination with jute fibre mats to produce composites by a film stacking technique. The tensile properties of composites produced at temperatures in the 180–220°C range were significantly higher than those of polylactide alone. Composite samples failed in a brittle fashion under tensile load and showed little sign of fibre pull-out. Examination of composite fracture surfaces using electron microscopy showed voids occurring between the jute fibre bundles and the polylactide matrix in some cases. Size exclusion chromatography revealed that only minor changes in the molecular weight distribution of the polylactide occurred during the process. A study by Suesat et al.51 examined the influence of processing parameters on the physical properties and structure of yarns constructed from poly(llactic acid) (PLLA) fibres. Commercially produced spun- and false-twist texturized (FTT) PLLA yarns and their knitted fabrics were characterized for their tensile properties and structural features using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. The effects of predye heat-setting at 130°C for varying times were assessed in terms of the resultant tensile properties of the yarns. As-received FTT yarns (and hence their derived fabrics) differed in properties and fibre microstructure compared to the spun yarns (and fabrics). Both the onset and completion of melting occurred at approximately 5°C higher for the spun yarn than for the FTT yarn (Fig. 16.17). More subtle differences were also evident: for example, the endotherm for the FTT yarn was narrower than that for the spun yarn. Overall, the as-received spun and false-twist texturized PLLA yarns displayed differences in both tensile properties and morphology, which the authors attributed to the differences in yarn-formation routes. More significantly, for both FTT and spun materials, differences in fibre properties and structure were observed between yarns removed from the fabrics and their respective feed-yarns. The authors associated this with possible thermo-mechanical influences experienced by the fibres during the knitting process. The duration of heat-setting influenced the tensile properties and DSC spectra for both types of yarn. In a study by Lou et al.,52 a PLA multifilament was twisted using different twisting parameters in a rotor-twister to fabricate US Pharmacopoeia (USP) size 5-0 and 7-0 surgical sutures. The best tensile strengths were 3.1 and 12.3 N, and the coefficients of variation were 3.70% and 1.75%. The PLA suture was then scoured with 1 wt% sodium hydroxide to eliminate impurities; the knot-pull strength decreased to 1.66 and 6.84 N for 7-0 and 5-0 PLA sutures, respectively, but still conformed to the USP knot-pull strength standard. An in vitro hydrolysis test was performed at 37°C by immersing a 5-0 PLA
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1.5
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Spun yarn FTT yarn 120
16.17 (a and b) Hierarchical organization of a twisted or cabled yarn. Fibres are combined to form bundles, bundles to form strands, and strands to form cords.
suture in physiological saline (0.9 wt% NaCl aqueous solution); the knotpull strength decreased by 12% after 28 days. Several natural fibres have been used as sustainable yarns for technical applications. Jute yarn–Biopol® composites were prepared using a hot-press moulding technique by Mohanty et al.53 Two varieties of jute yarns (7.36 lb/ spy and 11.86 lb/spy) were used for composite fabrications. The mechanical
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properties, such as tensile strength, bending strength, impact strength and bending-E-modulus, increased substantially in comparison to those of pure Biopol® as a result of their reinforcement with jute yarns. The most remarkable observations included more than 150% enhancement in tensile strength, impact strength and bending-E-modulus. In another piece of research using banana fibre by Kumar et al.,54 fibrereinforced soy protein composites were manufactured. Alkali-modified banana fibres were characterized in terms of density, denier and crystallinity index. Soy protein composites were prepared by incorporating different volume fractions of alkali-treated and untreated fibres into soy protein isolate (SPI) with different amounts of glycerol (25–50%) as a plasticizer. The authors found that at 0.3 volume fraction, the tensile strength and modulus of alkali-treated fibre-reinforced soy protein composites increased to 82% and 96.3%, respectively, compared to soy protein film without fibres. The water resistance of the composites increased significantly with the addition of glutaraldehyde, which acts as crosslinking agent. The biodegradability of the composites was also tested in a contaminated environment and the composites were found to be 100% biodegradable.
16.7
Conclusion
There has been substantial research on biodegradable fibres and yarns and newer areas are being developed. Biodegradable fibres and yarns have applications in non-wovens, fabrics, bedclothes, wipes, wet tissues, medical items, interlinings, etc. Hydrolytically degradable polymers are generally preferred for implants due to their minimal site-to-site and patient-to-patient variations compared to enzymatically degradable polymers. Major applications for PLA yarn and non-wovens include clothing and furnishings such as drapes, upholstery and covers. Some exciting potential applications include household and industrial wipes, nappies, feminine hygiene products, disposable garments, and UV-resistant fabrics for exterior use (awnings, ground cover, etc.) among others. PLA polymers, which have shown much promise, could be used in a number of unexplored applications by replacing the conventional polymers, where they can contribute a significant role in the form of composites, copolymers and blends for different applications. More research needs to be directed at producing PLA at a lower cost than that of other plastics. Fibres spun from biodegradable materials have been used as matrices for tissue engineering applications. The fast-growing field of tissue engineering, or tissue regeneration, can be considered as an outgrowth of the absorbable polymer technology. Tissue engineering relies mainly on the use of an absorbable scaffold that undergoes mass loss along with tissue formation to replace the absorbing scaffold. However, in spite of the availability
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of a broad range of absorbable polymers, their conversion to an easily sterilizable scaffold, having the proper microporosity that optimally allows cell propagation and removal of metabolic by-products, is yet to be realized. Biopolymers, unlike synthetic polymers, also suffer from the fact that their uniformity varies (batch to batch variation is quite high) and cannot be positively controlled.
16.8
References
1. A.-M. Clarinval and J. Halleux, ‘Classification of biodegradable polymers’, in Biodegradable Polymers for Industrial Applications, edited by Ray Smith, CRC Press, Boca Raton, FL, and Woodhead Publishing, Cambridge, UK, 2005. 2. Q. Wang, N. Zhang, X. Hu, J. Yang and Y. Du, European Journal of Pharmaceutics and Biopharmaceutics, 66(3), June 2007, 398–404. 3. G. Schmack, D. Jehnichen, R. Vogel and B. Tändler, Journal of Polymer Science Part B: Polymer Physics, 38(21), 2841–2850. 4. A. K. Schneider, US Patent 3,636,956, 1972. 5. B. Eling, S. Gogolewski and A. Pennings, Polymer, 23, 1982, 1587. 6. S. H. Hyon, K Jamshidi and Y. Ikada, in Polymers as Biomaterials, edited by S. Shalaby, A. S. Hoffmann, B. D. Ratner and T. A. Horbett, Plenum Press, New York, 1984, p. 51. 7. G. Schmack, B. Tändler, R. Vogel, R. Beyreuther, S. Jacobsen and H. G. Fritz, Journal of Applied Polymer Science, 73, 1999, 2785–2797. 8. B. Gupta, N. Revagade and J. Hilborn, Progress in Polymer Science, 32(4), April 2007, 455–482. 9. X. Yuan, A. F. T. Mak, K. W. Kwok, B. K. O. Yung and K. Yao, Journal of Applied Polymer Science, 81, 2001, 251–260. 10. Y. Nishimura, A. Takasu, Y. Inai and T. Hirabayashi, Journal of Applied Polymer Science, 97, 2005, 2118–2124. 11. X. Yuan, A. F. T. Mak, K. W. Kwok, B. K. O. Yung and K. Yao, Journal of Applied Polymer Science, 81, 2001, 251–260. 12. S. Gogoloewski and A. Pennings, Journal of Applied Polymer Science, 28, 1983, 1045. 13. K. W. Leenslag and A. J. Pennings, Polymer, 28, 1987, 1695. 14. A. R. Postema, A. H. Luiten and A. J. Pennings, Journal of Applied Polymer Science, 39, 1990, 1265–1274. 15. M. Yokoichi, M. Chatani, H. Tadokoro, K. Teranishi and H. Tani, Polymer, 14, 1973, 267–272. 16. M. Kunioka, A. Tamaki and Y. Doi, Macromolecules, 22, 1989, 694–700. 17. S. Bloembergen, D. Holden, G. K. Hamer, T. L. Bluhm and R. H. Marchessault, Macromolecules, 19, 1986, 2865–2871. 18. G. Schmack, D. Jehnichen, R. Vogel and B. Tändler, Journal of Polymer Science: Part B: Polymer Physics, 38, 2000, 2841–2850. 19. T. Iwata,Y. Aoyagi, M. Fujita, H. Yamane, Y. Doi, Y. Suzuki, A. Takeuchi and K. Uesugi, Macromolecular Rapid Communications, 25, 2004, 1100–1104. 20. J.-M. Park, D.-S. Kim and S.-R. Kim, Composites Science and Technology, 64(6), May 2004, 847–860.
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21. K. H. Lee, H. Y. Kim, M. S. Khil, Y. M. Ra and D. R. Lee, Polymer, 44(4), February 2003, 1287–1294. 22. F. Yang, R. Murugan, S. Wang and S. Ramakrishna, Biomaterials, 26(15), May 2005, 2603–2610. 23. X. Zong, K. Kim, D. Fang, S. Ran, B. S. Hsiao and B. Chu, Polymer, 43(16), July 2002, 4403–4412. 24. Z. Ge, J. C. Goh, L. Wang, E. P. Tan and E. H. Lee, Journal of Biomaterials Science, Polymer Edition, 16(9), 2005, 1179–1192. 25. B. X. Fu, B. S. Hsiao, G. Chen, J. Zhou, I. Koyfman, D. D. Jamiolkowski and E. Dormier, Polymer, 43(20), September 2002, 5527–5534. 26. M. Deng, G. Chen, D. Burkley, J. Zhou, D. Jamiolkowski, Y. Xu and R. Vetrecin, Acta Biomaterialia, 4(5), September 2008, 1382–1391. 27. M. Deng, J. Zhou, G. Chen, D. Burkley, Y. Xu, D. Jamiolkowski and T. Barbolt, Biomaterials, 26(20), July 2005, 4327–4336. 28. X. Zhang, T. Liu, T. V. Sreekumar, S. Kumar, X. Hu and K. Smith, Polymer, 45(26), December 2004, 8801–8807. 29. P. Miaudet, C. Bartholome, A. Derré, M. Maugey, G. Sigaud, C. Zakri and P. Poulin, Polymer, 48(14), June 2007, 4068–4074. 30. J. Fei and L. Gu, European Polymer Journal, 38(8), August 2002, 1653–1658. 31. M. Jiang, X. Song, G. Ye and J. Xu, Composites Science and Technology, 68(10–11), August 2008, 2231–2237. 32. Y. Zhang, W. Sun, Z. Li, X. Zhou, Eddie, and C. Chau, Construction and Building Materials, 22(3), March 2008, 370–383. 33. S. A. S. Akers, J. B. Studinka, P. Meier, M. G. Dobb, D. J. Johnson and J. Hikasa, International Journal of Cement Composites and Lightweight Concrete, 11(2), May 1989, 79–91. 34. K. G. Satyanarayana, G.G.C. Arizaga and F. Wypych, ‘Biodegradable composites based on lignocellulosic fibers – an overview’, Progress in Polymer Science, 2008, doi:10.1016/j.progpolymsci.2008.12.002. 35. V. A. Alvarez, R. A. Ruseckaite and A. Vázquez, Polymer Degradation and Stability, 91, 2006, 3156–3162. 36. V. A. Alvarez and A. Vázquez, Polymer Composites, 25, 2004, 280–288. 37. M. Miraftab, Q. Qiao, J. F. Kennedy, S. C. Anand and G. J. Collyer, ‘Advanced materials for wound dressings: biofunctional mixed carbohydrate polymers’, in: Medical Textiles, edited by A. C. Anand, Woodhead Publishing, Cambridge, UK, 2001, pp. 164–172. 38. M. Miraftab, Q. Qiao, J. F. Kennedy, M. R. Groocock and S. C. Anand, ‘Advanced wound care materials: developing an alginate fibre containing branan ferulate’, Journal of Wound Care, 11(9), 2002, 353–356. 39. C. J. Knill, J. F. Kennedy, J. Mistry, M. Miraftab, G. Smart, M. R. Groocock and H. J. Williams, Carbohydrate Polymers, 55(1), January 2004, 65–76. 40. L. Fan, Y. Du, B. Zhang, J. Yang, J. Zhou and J. F. Kennedy, Carbohydrate Polymers, 65(4), September 2006, 447–452. 41. S. Luo and A. N. Netravali, Journal of materials science, 34, 1999, 3709–3719. 42. M. Shibata, K.-I. Takachiyo, K. Ozawa, R. Yosomiya and H. Takeishi, Journal of Applied Polymer Science, 85(1), 2002, 129–138. 43. S.-H. Lee and S. Wang, Composites Part A: Applied Science and Manufacturing, 37(1), January 2006, 80–91. 44. R. L. Horan, A. L. Collette, C. Lee, K. Antle, J. Chen and G. H. Altman, Journal of Biomechanics, 39, 2006, 2232–2240. © Woodhead Publishing Limited, 2010
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45. A. Hokugo, T. Takamoto and Y. Tabata, Biomaterials, 27(1), January 2006, 61–67. 46. M. Q. Zhang, M. Z. Rong and X. Lu, Composites Science and Technology, 65(15–16), December 2005, 2514–2525. 47. J. M. Schakenraad, J. A. Oosterbaan, P. Nieuwenhuis, I. Molenaar, J. Olijslager, W. Potman, M. J. D. Eenink and J. Feijen, Biomaterials, 9(1), January 1988, 116–120. 48. M. Wollerdorfer and H. Bader, Industrial Crops and Products, 8(2), May 1998, 105–112. 49. T. Nishino, K. Hirao, M. Kotera, K. Nakamae and H. Inagaki, Composites Science and Technology, 63(9), July 2003, 1281–1286. 50. D. Plackett, T. L. Andersen, W. B. Pedersen and L. Nielsen, Composites Science and Technology, 63(9), July 2003, 1287–1296. 51. J. Suesat, D. A. S. Phillips, M. A. Wilding and D. W. Farrington, Polymer, 44(19), September 2003, 5993–6002. 52. C.-W. Lou, C.-H. Yao, Y.-S. Chen, T.-C. Hsieh, J.-H. Lin and W.-H. Hsing, Textile Research Journal, 78(11), 2008, 958–965. 53. A. K. Mohanty, M. A. Khan, S. Sahoo and G. Hinrichsen, Journal of Materials Science, 35(10), May 2000, 2589–2595. 54. R. Kumar, V. Choudhary, S. Mishra and I. Varma, Frontiers of Chemistry in China, 3(3), September 2008.
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Yarn and fancy yarn design using three-dimensional computer graphics and visualisation techniques
W. T a n g, University of Teesside, UK and T. R. W a n, University of Bradford, UK
Abstract: This chapter describes methods for simulating yarn structures using three-dimensional computer graphics techniques. A mathematical model is derived, which reproduces the general microstructure of yarns and is then extended to that of fancy yarns. The chapter also introduces the current state-of-the-art methodologies in cloth simulation and modelling with reference to both computer graphics and textile communities. A 3D visualisation framework is presented, as well as simulation examples in comparison with authentic samples of yarns. Key words: yarn and fancy yarn microstructures, 3D computer visualisation, textile design, geometrical modelling.
17.1
Introduction
Textile yarns are the basic elements of fabrics. For fabric design and production, yarns are mainly considered in terms of their colours, structures and material properties. Colours and the structure of yarns contribute to the fabric texture, covering power, lustre and thickness. The yarn design process is time-consuming and costly, especially the design of fancy yarns which requires much more intricate work in both design and sample-making processes. The rapid development of computer graphic techniques in terms of both computer software and hardware now allows innovative methods for the design of yarns including fancy yarns, improving the design efficiency and cutting sampling costs. Early work [1, 2] on the design and simulation of yarn structures was mainly concerned with image representations in twodimensional imagery for the colour and texture of yarn elements. In this work, two-dimensional patterns of yarn primitives in forms of colour and 2D shape of the elements had been stored into the computer system for designers to select. A design process was implemented by selecting colours and shapes of yarn elements. These 2D methods may have been efficient in designing and simulating surface appearances and colours of yarns or even fancy yarns. Because natural structures of yarns are geometrically three-dimensional, two568 © Woodhead Publishing Limited, 2010
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dimensional computer representations are somewhat restrictive in providing necessary detailed structural information about yarns. Three-dimensional computer graphics and computer-aided design (CAD) techniques have been providing possibilities to represent objects to be visualised and designed in virtual reality environments in greater details. Despite the advances in 3D computer graphics technologies, little attempt has been made concerning three-dimensional computer-aided design of yarns and fancy yarns, especially 3D visualisation and design of three-dimensional structures of yarns. One of the reasons for the relatively slow progress in these areas in the textile industries may be partially due to the lack of suitable methodologies to describe geometric structures of yarns and fancy yarns in computer graphics terms, as well as to the lack of a general approach using sophisticated 3D computer graphics techniques to be applied to textile engineering applications. In this chapter first we review the state-of-the-art of 3D computer graphics and visualisation technologies for textile design and visualisation. We show that simulations of cloth/clothes and animated effects of cloth and fabrics on moving virtual characters are also important aspects to 3D computer graphics applications, such as computer games. In the past, for cloth simulations, the computer science community has focused mainly on computing dynamic motions of cloths with geometric polygon meshes, without detailed modelling and simulating microstructures of yarns and fancy yarns. Only recently have there been a limited number of attempts at trying to incorporate properties of these microstructures into cloth simulations [3]. In contrast, modelling and simulating yarns and fancy yarns at the microstructural level are largely omitted in computer simulations of cloths in the computer science community, and the need to address the properties of simulated cloth at yarn level has only recently received some research attention. A study by the authors into developing a general modelling and simulation framework and the methodology for yarn and fancy yarn design and visualisation by using 3D computer graphics technology is demonstrated. A general yarn geometrical model is presented for 3D modelling purposes. On the other hand, fancy yarn structures consist of one or more basic yarn primitives with various structural features which provide fine details of the yarn structures. The irregularity of fancy yarns can be created by designing and changing the curvature of the central axes and the shapes of the crosssections of these yarn primitives. A general framework for mathematical modelling of yarn and fancy yarn structures is presented below. The 3D mathematical descriptions are applied to computer simulations and representations of yarns and fancy yarns in a 3D computer graphical design system. Any CAD system must provide a user interface in order to facilitate design processes. A set of user interface components and functionalities of these system components is presented and the developed 3D yarn design and visualisation system is shown to be capable of designing complex yarn
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structures with photo-realistic representations of various yarns. With this system, a designer’s original ideas could be created, modified and visualised on a computer screen before beginning the sample making process. Finally, future challenges in the development of textile CAD systems for yarns are described, bearing in mind that designing cloth and fabrics is the final goal of designing yarns.
17.2
3D computer graphics and visualisation technologies for cloths and yarns
Most of the research in cloth simulations using 3D computer graphics technologies has focused on woven fabric [4–6]. These simulations generally model mechanics of the woven cloth as linear elastic sheets. Typically, for simplicity, spring-mass models are employed to compute the internal linear elastic forces applied on cloth nodes. As shown in Fig. 17.1(a), a grid is used to construct a piece of woven fabric, in which each node of the grid is treated as a particle. Internal spring forces and any external forces acting on these particle nodes derive the mechanics of the cloth. As demonstrated in Fig. 17.1(b), three kinds of springs are used in most cloth simulation models to date. Directly connected springs simulate stretch properties of the cloth, diagonally connected springs simulate sheer, and indirectly connected springs model the bending of the cloth. Figure 17.2 shows a 3D virtual reality simulation of cloth using the above modelling principles [6]. Spring-mass models are capable of simulating small in-plane deformations of woven cloth, which can often achieve acceptable realism for woven fabric in computer graphics applications, such as computer games. However, these models do not take into account the structure of yarns. Cloth is made of yarns.
(a)
(b)
17.1 (a) A grid system consists of a set of particles used to construct woven fabric structures. (b) Three types of springs indicated by double arrows connecting particles are used to model spring-mass properties of the fabric dynamics.
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17.2 A virtual environment for a fashion show with 3D computer graphics simulated cloth [6].
If computational cost is permissible, modelling yarns in cloth simulation is essential in the field of cloth engineering, and it is also desirable in computer graphics applications. Perhaps the earliest work in modelling yarn structures was carried out by Peirce, who derived a set of parameters and equations for modelling crosssections of yarns in a woven fabric as inextensible curves [7]. Kawabata et al. proposed a beam and truss model for yarn crossings in a woven fabric, as well as measurements for the physical force curves resulting from stretch [8]. In the textile community, researchers used variations of the beam-and-truss models for plain-woven fabrics [9, 10]. For woven fabric, there are two set of yarns, the warp and the weft, organised into two perpendicular directions in the fabric. Yarns in knitted fabrics are organised into a regular set of loops in horizontal rows, interlocked along the vertical directions, called wales. In the cloth industry, knitted fabrics are also common products that are used just as much as woven fabrics. Because knitted fabrics are more complex than woven fabrics, they have been less well studied. Tang modelled the configuration of yarn structures in weft knitted fabrics as inextensible 3D parametric tubes [11]. Two control parameters were introduced to control the shape of a loop segment, while maintaining the loop geometry symmetry and smoothness. A knitted fabric is the construction of the loops according to the principles of weft knitting, the geometrical constraints imposed by the loop interlacing contact and the assumptions made about the yarn and fabric to be simulated. There are also boundary conditions, where the graphical © Woodhead Publishing Limited, 2010
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representation of the design of the fabric structure or the change of the shape of the loop must be obeyed. A CAD system was developed for designing and simulating weft knitted fabric based on 3D computer graphics techniques. Figure 17.3 shows a screen capture of a simulated plain weft knitted fabric produced by the system, and Figs 17.4(a) and (b) demonstrate a simulated single-jersey jacquard weft knitted fabric produced by the system in technical face and back, respectively [12]. More recently, Kaldor et al. [3] proposed a simulation model for modelling the motion of yarns in weft knitted fabric as an inextensible B-spline tube and produced complex dynamic motions of knitted fabrics. The design of yarn and fancy yarn structures has not received much research attention. In this chapter, a systematic approach to the modelling and simulation of yarn and fancy yarns at a microstructural level is described.
(a)
(b)
17.3 (a) Four simulated loop structures, and (b) a simulated plain weft knitted fabric produced by the system [11].
(a)
(b)
17.4 A single-jersey jacquard weft knitted fabric produced by the system [11]: (a) technical face; (b) technical back.
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Microstructures of yarns and fancy yarns
In the textile industry, yarns are produced by blending a large number of fibres or filaments, and then twisting them together to deliver the strength and length of the yarn. Generally speaking, a characteristic of yarn structures is that they have much greater length compared to their thickness. Combining a certain number of fibres, usually by applying a twisting operation, results in a low-level yarn, which is a so-called single yarn. A much higher level of yarn microstructure can be produced by twisting several single yarns together to produce a ply yarn. Fancy yarns, in contrast with the yarns described above, have specially designed features of irregularities within their structures or random variations along the length to give a novel structural appearance, for instance irregularities of cross-sections along the length of the yarn. According to the principles of fancy yarn production, any fancy yarn may consist of one or more foundation yarns which provide the yarn structure around which the effect yarn may twist, curl, loop, etc. There are some typical types of fancy yarns. Some fancy yarns have quite similar structures to ordinary ply yarns but contain different colours or diameters of single yarns. Some fancy yarns have a more novel appearance. The structure of this kind of yarn can be subdivided into core yarn and effect yarns. The core yarn is in the middle of the structure with different twist or diameter, whereas effect yarns twist around the core in various ways to give the fancy effects. A study by the authors has tried to present a method for 3D computer modelling and visualisation of both yarns and fancy yarns [11] . The modelling and representation are an explicit representation of the subdivisions of the structures of the yarns and the fancy yarns. The internal geometric structure of an ordinary yarn has been theoretically studied by many researchers. Electron microscopic equipment has provided a great deal of information about the internal structures of yarns. Figure 17.5 shows a computer-generated example of a three-ply yarn with its cross-section, forming a typical tyre-cord construction. The key features of yarns are the twist level and cross-sectional variations. Therefore, modelling the structure of yarn has been based on simulating the twist effects and cross-sections of yarns [12].
17.4
Mathematical modelling of yarn and fancy yarn structures
A yarn or a fancy yarn has a complex microstructure due to the large number of constituent fibres with various properties such as fibre fineness, elasticity, etc. As the diameter of a single fibre is in the order of micrometres, it has a very low opacity and is not often perceivable individually; only the collection
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Technical textile yarns P2
C2
P3
P2
b2
P3 P3
P2
a2
a3 b3
b1
C3
C1
P1 a1
P1
P1 (b)
(a)
17.5 (a) A computer generated example of three-ply yarn; (b) crosssection of the yarn.
of fibres and their spatial arrangement determine the visual impression of yarns. Fibres at the core of yarns tend to have little relative movement, and the yarn as a whole resists stretching. A geometric model representing each single fibre would be considered too costly and unnecessarily detailed for generating the mechanical properties of yarns; however, the visual appearance of the yarn structure might be of interest to computer graphical simulations of cloth, especially for weft knitted clothing. A simulation model that models surface data sets of the yarns and fancy yarns in order to provide a visual realistic appearance of yarn structures has been developed by the authors. However, finely detailed rendering of fibres of the yarn surface appearance by using advanced computer graphics rendering techniques is beyond the scope of this chapter. Readers are referred to Chen et al. [13] and references therein on cloth rendering techniques. Instead, the focus of the discussions will be on modelling the yarns as inextensible 3D geometrical structures with a larger number and higher density of surface points to approximate a smoother surface-rendering effect of the yarn. This approach can incur a relatively low cost in computing time and rendering, and produce a reasonably realistic representation of various yarn structures.
17.4.1 3D mathematical descriptions of yarn structures The geometrical structure of yarn is generally modelled by three-dimensional parametric curves. The 3D curve is employed as the central axis of the simulated yarn. In principle, the surface of the yarn can be generated by sweeping a yarn cross-section along the 3D curve. Figure 17.5(a) shows a three-ply yarn generated by the system. Fibres in each single yarn are first twisted about the central axis of each individual single yarn. The cross-sections of the
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single yarns or yarn primitives as shown in Fig. 17.5(b) are denoted as C1, C2 and C3, which are first twisted and then swept along each yarn’s central curve axis individually. After that, the whole assembly of yarn primitives is twisted together to produce a ply yarn. The duration of twist within the single yarn is therefore normally different from that of the ply yarn. In this approach, the central curve of the yarn can be mathematically described as a three-dimensional double helix, as shown in Fig. 17.6. The parameters x, y and z refer to coordinates along the central axis of the yarn in the respective duration, and t is the twist angle. Without loss of generality, all vectors are normalised by dividing their terms by the yarn diameter d. The following relations describe the global coordinates of the points on the surface of the yarn, which are regarded to be the structural parameters of yarns: L n
x=
y = A cos t
z = A sin t
0 ≤ t ≤ 2π
17.1
In equation (17.1), L equals l/d, l is the unit length of the yarn, n is the number of turns per unit, and A is the amplitude of the central axis of the yarn. y
C1 C2
Yt
C3
Xt Pt
Zt
C1 C3
C2
x
z
17.6 The three-dimensional double helix and twist structure of threeply yarn.
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The coordinate system is defined as follows: at each point along the central curve, say a point Pt, the cross-section of the yarn is perpendicular to the tangent of the curve at the point. A local coordinate system Xt, Yt, Zt may be defined with the Yt axis coinciding with the tangent direction at point Pt and the Xt, Yt and Zt axes being mutually orthogonal. We denote the points on the surface of a yarn as P(i, j, t), where i indicates that the corresponding point belongs to the surface of the ith single yarn, j indicates the point j on a cross-section of the single yarn, and t indicates the location of the single yarn cross-section along the central axis of a single yarn. The position of each surface point in a fixed coordinate system OXYZ, i.e. the global coordinate system, is calculated by a set of transformation matrices by transforming the positions of these surface points in terms of the local coordinate system OtXtYtZt. The method is first to make the local coordinate axes Xt, Yt, and Zt have the same directions as the fixed coordinate axes X, Y and Z by rotating them respectively, and secondly to translate the origin of the local coordinate system to the origin of the fixed coordinate system. After the above rotation and translation procedures, the coordinates of the surface points in the local system are converted into the coordinates of the points in the global system. Letting matrix [Pt] represent the coordinates of the surface points at the local system and matrix [P] represent the coordinates of the surface points at the global system the relation between the two coordinate systems is determined by equation (17.2):
[P] = [Rx][Ry] [Rz] [Txyz] [Rt]
17.2
where [Rx], [Ry] and [Rz] are rotation matrices and [Txyz] is the translation matrix. At each transformation step, the cross-section of the yarn lies on the plane formed by points PtXtZt, which is perpendicular to the tangent of the central curve at point Pt in the local coordinate system. If R indicates the diameter of the ply yarn, and r1, r2, and r3 are the diameters of each single yarn in the yarn structure with cross-sections denoted by c1, c2 and c3 respectively, then the coordinates of the central points of the cross-sections are expressed as Pc1(Xc1(t), Yc1(t), Zc1(t)), Pc2(Xc2(t), Yc2(t), Zc2(t)) and Pc3(Xc3(t), Yc3(t), Zc3(t)). The cross-section of the yarn is transformed from position 1 where t = t1 to position 2 where t = t2 by a twist angle f. Applying linear transformation gives equation (17.3): 2πnp = (t1 – t2) 17.3 T where T is the length of the yarn, t is the position of the yarn cross-section along the axis, and np is the number of turns in the ply yarn within the length T. The following boundary conditions are imposed at each transformation step that the cross-sections in the ply yarn must obey to avoid the single
f
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yarns overlying each other. These boundary conditions are based on the assumptions that yarns are inextensible 3D parametric tubes with minimum compression. For simplicity, vector notations are used to describe the boundary conditions, as shown in equation (17.4): Pc1 – Pc 2 ≥ r1 + r2; Pc1 – Pc 3 ≥ r1 + r3; Pc 3 – c 2 ≥ 3 + 2 17.4 To generalise the boundary conditions presented P Pin equation r r (17.3) for describing other ply yarns, such as five or seven ply yarn, equation (17.4) can be rewritten as equation (17.5) by introducing two indices i and j, indicating the ith and jth single yarns in the ply-yarn structure: Pci – Pcj ≥ ri + rj , i, j = 1, 2, … N , i ≠ j 17.5 where N is the total number of single yarns in the ply yarn. The modelling process described above offers a general mathematical framework to simulate ply yarns comprised of various numbers of single yarns. The next subsection demonstrates how to build on the general framework to further develop a methodology to model unique features of fancy yarn structures, again through the use of mathematical descriptions about variations of the geometric structures of fancy yarns.
17.4.2 Modelling irregularities of fancy yarn structure Fancy yarn structures are manifested in terms of irregularities of curvatures of the central yarn axis and changes in the diameters of cross-sections in the yarns. To take into account the geometric features of fancy yarns, two types of scale functions for modelling the irregularities of the fancy yarn structure are introduced into the mathematical model for yarns described in the previous section. We first design a new function called the twist scale function, which is a function of an angle variable. The changes of the twist angle along the central curve of the ply yarn are further modelled using parameters defined as the scaling factor, the angular velocity and the angular acceleration. The angular velocity and angular acceleration control the length and frequency of the changes. Hence, the twist scale function is a parameter-dependent function related to twist angles and the length of the central curve of the yarn. This type of function can also be referred to as an angular scale function as expressed in equation (17.6):
fs = a f (t, T )
T = wt
17.6
where a is the changing rate of the yarn central axis, normally a = 2πn/T, t is the sweeping position of the yarn cross-section, w is the angular velocity
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of the central curve at t, and the T is the period of the twist angle changing along the length of the central curve. A second function called the shape scale function is introduced, which is applied to the cross-sectional shapes of the single or ply yarns. The scaling factor controls the change of diameter the of cross-sections of yarns. This type of function is a parameter-dependent function related to the diameter of the yarn and the length of the central curve of the yarn, and is referred to as a diameter scale function as expressed in equation (17.7):
fd = bf (t, T )
T = wt
17.7
where b is the cross-sectional scaling factor, t is the sweeping position of the yarn cross-section, and T is the period of the twist angle changing along the length of the central curve. As can be seen, the twist scale function is a parameter-dependent function which controls the twist angle of the yarn at the current position and could be changed along the length of the yarn central curve. In order to describe the irregularities occurring along the length of the yarn in terms of the changes in the twist angles, 2D curves are employed to express the profile of the irregularity features. For example equation (17.6) is the angle scale function representing the changes of the twist angle of the effect yarn along the length of the yarn central curve. If fs = a(t, T) = a0 t and letting t change within the range [0 ≤ t ≤ T], as the scale function is a constant a0 along the length of the yarn, the twist angles of the single yarn will not change and will remain as a0 along the length of the yarn. If we let f(t) be the twist angle at position t, and f(t0) be the twist angle at position t0, we have:
f(t) = f(t0) ¥ a0(t – t0, T )
17.8
where T is the period of the twist angle change along the central curve. Similarly, the second type of scale function, the cross-section shape function, is used to model the irregularity of the shape of cross-sections of the yarn, for example simulating the shape of cross-sections of the core yarn or effect yarns that comprise the fancy yarn. This kind of scale function is also a parameter-dependent function which controls the shapes of the crosssections of the core yarn or effect yarn along the length of the yarn central curve. If we let r(t) be the distance between the current surface point and the central axis of the yarn at transformation position t, and r(t0) be the distance between the surface point and the central axis of the yarn at the transformation position t0, we have a general form as shown in equation (17.9)
r(t) = r(t0) ¥ b0(t – t0, T )
17.9
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As described above, 2D curves are employed by the scale functions to simulate the irregularity of the cross-sections. Figure 17.7 illustrates two examples of 2D profiles for simulating the twist angular irregularities. With the description in Fig. 17.7(a), the twist angle of the single yarn will remain as a0 through the course of T, whereas using the profiles expressed in Fig. 17.7(b), the cross-section of the yarn is transformed from position t0 to position t by applying a twist angle f, which is varied non-linearly along T. Thus, the scale function can be described in this case by the following set of equations: Ïa f ((t – t 0 ), T ) = a 0 t 0 ≤ t ≤ t1 Ô fs = Ìa f ((t – t 0 ), T ) = a 0 sin t t1 ≤ t ≤ t 2 17.10 Ôa ((t – t ), T ) = a ≤ ≤ t t T 0 0 2 Ó f Equation (17.10) describes the increase of the twist angle following a path corresponding to a sine function for the length of the yarn between t1 and t2; and before t1 and after t2 no twist angular irregularities occur in the yarn. Although, here only two examples of the simulation are demonstrated, more complex 2D curves can be employed to approach more realistic representations of fancy yarns. Figure 17.8 shows four examples of computer generated yarns and Fig. 17.9 shows a comparison between a computer generated fancy yarn with an actual fancy yarn sample. Table 17.1 shows the parameters used for yarn simulation.
17.5
Descriptions of a computer aided design (CAD) system for yarn and fancy yarn structures
The method described here is implemented in the form of a 3D CAD system. The solid representation is achieved using computer graphics techniques to represent surface properties of the object with desirable representation of fs
fs
t0
T (a)
t
t0
t1
17.7 Two examples of cross-sectional profiling.
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(b)
t2
T
t
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17.8 Yarn and fancy yarn structures generated by the CAD system [12].
17.9 Comparison of computer generated yarn structures (second and fourth rows) with real yarn samples (first and third rows).
light reflections on the surfaces, including the treatment of translucent solids and the creation of shadows produced by various light sources, and dealing also with the hidden line and surface removal problems. The models of
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Table 17.1 Parameters used for yarn simulation Type of simulation
Single yarn diameter (cm)
Ply-yarn diameter (cm)
Single yarn twist (degrees)
Ply-yarn twist (degrees)
Type Type Type Type
0.18, 0.06 0.06 0.06 0.5, 0.03
0.52 0.18 0.18 0.8
10.05 5.5 5.5 20.8
20.8 12 12 20.8
A B C D
yarn and fancy yarn structures have been represented as 3D photo-realistic models which can be enlarged, transformed and rotated through any angle in a three-dimensional coordinate system. Surface properties of the yarn can be adjusted according to rendering parameters. The values of emission, spectrum, diffusion, shininess and transparency of the yarn and fancy yarn models can be adjusted to achieve the best appearance under the conditions of the available surface properties provided by the specific computer graphics software and hardware. The results show that this is a promising approach in the development of 3D CAD techniques for the design and visualisation of the structures of yarn and fancy yarn. These interfaces allow changes to be made to the structures of yarns and fancy yarns in terms of the structural parameters, colours, the surface shading effect, magnification, transformation and rotation of the object in a virtual way. The CAD system for the 3D design and visualisation of the structures of yarns and fancy yarns comprises three simulation modules that are integrated together to provide modelling, visualisation of the yarn and fancy yarns, and user interactions with the system in real-time. The modelling module of the CAD system comprises a number of program components for data initialisation, the initialisation of transformation matrices, and geometric computations for the central curve and vertices on the cross-section of the yarns. This program module computes the generalised models of the three-dimensional structures of the yarns and fancy yarns to give realistic representations of the structures. The visualisation module of the system initialises the rendering parameters, including surface normal computations and the initialisation of the surface properties for shading using Phong’s illumination model [14]. Functional program structures are constructed linked with each rendering component, such as the lighting editor and the material editor, which have been incorporated into the application system to provide user interfaces for designing and simulating the surface material properties of the yarn, and lighting effects. In order to include details of surface features of the yarn to make the yarn look more realistic by means of the effects of shading, the shading effects on the surface of the yarn were generated by applying a lighting model on the visible faces of the yarn. To do this it is necessary to
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calculate the normal vector to each of the faces. The surface of the yarn is approximated by a large number of small flat polygons; the normal direction to these is discontinuous across the polygon boundaries. In such a case, if the normal vectors are used to approximate the surface of the yarn it will appear faceted. This can be overcome by using a normal average method, in which the normal at the joint between neighbouring triangular polygons is replaced by the normalised average normal of the neighbour vertex normal. Yarns and fancy yarns have fine microstructures where single fibres are not perceivable by themselves but provide an important contribution to the overall visual impression of the yarn structure. To achieve better shading effects on the surface of yarns, an anisotropic lighting model consisting of specular reflection, internal reflection and diffuse reflection was used for simulating the surface properties of the yarn. The shading model is similar to the geometric model in that it does not precisely simulate the behaviour of light and surface in the real world but only approximates actual conditions. The shading model can also simulate the material properties applied. This material function plus lighting defines the current material for the object and sets several components of the material which affect the diffusion of the colours, and the shininess and transparency of the yarns generated. By adjusting the values of these corresponding parameters, different material properties of the yarn can be visualised. The system offers users the ability to interactively design and visualise the yarn and fancy yarn objects in a real-time interactive virtual environment, in which the object can be zoomed and transformed to any position in the virtual environment and can be rotated through angles within the design space. It provides user-friendly interfaces for designing yarns and fancy yarns in terms of the colour of each single yarn and the structural parameters, and for selecting and designing the irregularities within a fancy yarn. In this study, the system was programmed in C++ using IRIS Inventor graphics supporting software. We developed a set of Xt window communication system functions for setting up menus and user interfaces. The third module of the CAD system, the user interface module, consists of a top bar menu system, providing four sets of pop-up menus as well as mouse button functions for selecting the design objects and operating design tasks. On the top-bar popup menu system, there are mode design, colour design, structure design and knitted fabric design menus. The mode design menu is for selecting different rotation methods for visualising the yarn and fancy yarn objects. The colour design menu is used for opening a colour design sub-window system for selecting and applying various colour schemes from a colour palette to the yarns. This colour design system provides a colour design meter, colour indices and the colour map. The structure design menu is used especially for setting up design parameters for geometric structures of the yarn and fancy yarns. Similar to the structure design menu, the knitted fabric design
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menu offers functions to create a knitted fabric representation based on the designed yarn and fancy yarn structures. Figure 17.10 illustrates an overview of the CAD system and the interconnection between the above design and visualisation modules of the CAD system.
17.6
Conclusion
In this chapter, an approach to the 3D computer graphics modelling and representation of structures of textile yarns and fancy yarns is presented. The general mathematical model for modelling the geometric structures of yarns and fancy yarns that is described here allows realistic representations and visualisation of the yarn structures and is suitable for computer graphics modelling of yarns. Incorporated into the geometric model is also the data set for surface representations of the yarns to facilitate the design methodologies within an interactive CAD system using 3D computer graphics techniques. The geometrical descriptions of the internal configurations of ply yarns and fancy yarns are dependent on the compositions of the yarns and the geometrical details of the cross-sections of the yarns. The structures of the yarns can be generalised geometrically as cross-sections of yarns swept along the central axis of the yarns. In the computer graphics model the central axis of the yarn has been considered as a three-dimensional helix around which the surface of the yarn can be generated by two-dimensional geometric shapes, i.e. circles with defined diameters in this instance to be considered as the cross-sections of the yarn. Structural parameters
Structural design menu
Central curve parameters
Colour design menu
Fancy irregularity profile
Display window
Knitted fabric parameters
Pattern design Transformation matrices
Virtual trackball
Surface data
Lighting and shading parameters
17.10 Overview of the yarn CAD system.
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In order to simulate the irregularity of fancy yarns, the yarns are created by changing the path of the 3D central axis curves of effect yarns or a foundation yarn, as well as by varying the diameters of the cross-sections according to the settings of a fancy yarn production process. Two types of parameter-dependent scale function have been introduced to the general model, which can employ 2D curves for profiling the irregularities of the fancy yarns. According to the changes that occur along the length of the fancy yarn, complex 2D curves or functions can be designed to simulate various irregularities that are demonstrated in the fancy yarn design process. Fancy yarn structures can be represented realistically by using such simple profiling techniques. Interactive design and visualisation of the appearance and properties of yarns and fancy yarns within a real-time virtual environment provides a tool for the design of yarns or fancy yarns in terms of yarn structural parameters and colours, the composition of the ply yarn, and the irregularities of fancy yarns. The CAD system developed here, based on the modelling and simulation methodologies described, also offers a number of program functionalities for modelling yarn material properties and for simulating geometrical characteristics of yarns. Compared with the volume data rendering method, an alternative approach is taken to simulate the optical expression of a yarn surface for real-time rendering and low-cost computations for the interactive CAD system. The user-friendly design interface of the system provides users with a set of easy-to-use functions and program tools to design and visualise 3D structures of yarns and fancy yarns in realistic representations. These interfaces allow changes to be made to the yarns and fancy yarns in terms of structural parameters, colours, the surface shading effect, and manipulations in terms of zooming, translating and rotating the design objects in virtual reality. The general, geometrically based mathematical model for yarns and fancy yarns is applicable to modelling more complex yarn structures. However, it is worth mentioning that realistic rendering of the surface appearance of extreme types of fancy yarns is perhaps too complex, since the irregularities would take considerable computational time; in particular, the realistic surface rendering of knitted fabric with fancy yarns is still a challenge even with today’s modern computer graphics capabilities. The study presented in this chapter is essentially a geometric demonstration of the structures of yarns and fancy yarns. Further work should be carried out on modelling and simulating the physically based mechanical behaviour of yarns and fancy yarns in order to simulate the realistic behaviour of cloth and fabrics for the textile engineering field as well as computer graphics applications. The research work should be continued to incorporate the yarn and fancy yarn model into modelling and simulating fabrics for comprehensive textile design purposes.
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References
[1] Deng, Z.-M. and Yang, B., 1994, ‘Computer simulation of fancy yarns’, Journal of Textile Research, P. R. China, July. [2] Szczesny, C., Hardt, K. and Scheuffele, B. 1991, ‘Simulation of fancy yarns on screen’, International Textile Bulletin, Fabric Forming, 37 (Third Quarter). [3] Kaldor, J. M., James, D. L. and Marschner, S., 2008, ‘Simulating knitted cloth at yarn level’, ACM Transactions on Graphics (TOG), 27(3), August, SIGGRAPH 2008. [4] Baraff, D. and Witkin, A., 1998, ‘Large steps in cloth simulation’, in Proceedings of SIGGRAPH ’98, ACM Press, pp. 43–45. [5] Bridson, R., Fedkiw, R. and Anderson, J., 2002. ‘Robust treatment of collisions, contact and friction for cloth animation’, in Proceedings of SIGGRAPH ’02, ACM Press/ACM SIGGRAPH, pp. 594–603. [6] Stylios, G. and Wan, T. R., 1999, ‘The concept of virtual measurement’, International Journal of Clothing Science and Technology, 11(1), 10–18. [7] Peirce, F., 1937, ‘The geometry of cloth structure’, Journal of the Textile Institute, 28, T45–T97. [8] Kawabata, S., Niwa, M. and Kawai, H., 1973, ‘The finite deformation theory of plain-weave fabrics. Part I: The biaxial deformation theory’, Journal of the Textile Institute, 64, 21–46. [9] King, M., Jearanaisilawong, P. and Scorate, S., 2005, ‘A continuum constitutive model for the mechanical behavior of woven fabrics’, International Journal of Solids and Structures, 42, 3867–3896. [10] Zeng, X., Tan, V. B. C. and Shin, V. P. W., 2006, ‘Modelling inter-yarn friction in woven fabric armor’, International Journal for Numerical Methods in Engineering, 66, 1309–1330. [11] Tang, W. 1996, ‘Fancy yarn design and manufacture in a virtual real world’, Proceedings of Yarn and Fibre Science Joint Conference, Manchester, UK, December. [12] Tang, W., 1998, ‘Three dimensional computer aided design of weft knitted fabrics and yarns’, PhD thesis, School of Textile Industries, The University of Leeds, UK. [13] Chen, Y., Lin, S., Zhong, H., Xu, Y.-Q., Guo, B. and Shum, H.-Y., 2003, ‘Realistic rendering and animation of knitwear’, IEEE Transactions on Visualizations and Computer Graphics, 9, 43–55. [14] Phong, B., 1975, ‘Illumination for computer-generated pictures’, Communications of the ACM, 18(6), 311–317.
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Index
a-alumina Nextel 610 fibre, 363 abaca fibres, 558–9 abrasion resistance, 124–5, 216, 218, 220 absorbable sutures, 515–18, 528 list of examples, 516 acetone, 466, 483 acetylisation process, 308 acid phosphatase, 517 acrylic acid, 462 acrylic bulk yarns, 94 acrylic ester, 148 acrylics, 42 spun thread, 497 technical textile yarns coating, 148–9 thread finishing, 500 twisted multifilament thread, 498 adhesive-coated yarns, 177–8 adhesive laminating process, 176 adjustable BYPASS, 63 adsorption phenomena, 455 agar diffusion, 473 agrotech, 49, 53 Air-Com-Tex, 57 Air-Com-Tex 700, 60, 202 air-drag force, 123 air-entangled thread, 499 air-entangling process, 502 air-jet, 499 air-jet spinning core spun yarns production, 80 latest developments Murata Twin Spinner, MTS 881, 72 Roller Jet Spinner, 72 operation principle, 70–2 air-jet spun yarns, 126 air-jet texturing, 86, 199–201, 393–6 developments, 87–9 system principle and yarn structure, 395
thread, 499 air knife coating, 171 airbags, 510 alginate fibres, 557–8 alginate/chitosan fibre representation, 558 alginate–carboxymethyl chitosan blend fibres, 557 Allied Signal, 379 allylamine plasma glow discharge, 486 alumina–silica fibres, 363 aminopeptidase, 517 AMIspin, 77 ammonia plasma treatment, 486 Amoco, 355 analogue processing, 233 angular scale function, 577 angular velocity, 577 ANN see artificial neural network anti-electrostatic, 315 anti-stress yarn, 290 antiallergic yarn, 291 antibacterial, 315 antimicrobial coating, 287 antimicrobial treatment, 470, 472–6 antimicrobial yarns, 282–7 antimicrobials, 472 antistatic safety workwear, 511 antistatic yarn, 289–90 aqueous coating, 163–4 aramid fibres and yarns, 42, 370–7 applications, 377, 378 commercial products, 375–7 continuous filament yarns, 376 Kevlar 49, 29 yarn sizes, 376 spun yarns, 376–7 Teijinconex aramid spun yarns properties, 377 textured yarns, 377 composition and structure, 370, 372–3
586 © Woodhead Publishing Limited, 2010
Index
meta-aramid Nomex aramid fibre, 372 para-aramid Kevlar aramid fibre, 372 semi-crystalline polymers and paraaramid microstructure, 373 Technora aramid copolymer fibre, 372 future trends, 377 properties, 373–5 chemical resistance, 375 physical properties, 373–5 thermal properties, 375 aramid threads, 506–7 arc-PVD see cathodic arc deposition ARS core-spinning system, 76 artificial neural network simple model, 126 yarn hairiness modelling, 126–8 prediction performance, 127–8 AS/NZS 4399, 269 as-spun Kevlar aramid fibre, 373 ASTM 4935, 310 ASTM C 693, 330 ASTM D 578, 338, 339 ASTM D 696, 337 ASTM D 3823, 501 ASTM ES7, 311–12 specimen dimension, 312 Teflon specimen holders, 313 ASTM ES7-83, 312 ASTM ES7-84, 311 Astroquartz, 504 Astroquartz II sewing thread, 504 Australian/New Zealand Standard, 268, 269 auto-calibration, 241 autoclave moulding, 406–7 Autocoro 360, 64, 65, 66 Autocoro 288 rotor spinner, 63 automated multi-directional sewing threads, 502 auxetic yarns, 287–8 auxiliary winding, 319 azadirachtin, 473 B. mori silk, 478 b-hydroxyquinol, 481 bamboo fibre, 205, 286–7, 559 bamboo kun, 286–7 barberpole, 390 Barco solutions, 253–4 BarcoProfile, 253
587
air-jet texturising application, 253–4 rotor spinning machines application, 253 Barre effect, 124 basalt fibres and yarns, 365–70, 505 applications, 370 commercial products, 368–70 composition range, 367 continuous filament yarns, 370 rovings, 368 textured yarns, 370 composition and structure, 365, 367 future trends, 370 properties, 367–8 chemical durability, 368 chemical resistance, 367–8 comparative physical properties with other inorganic fibres, 368 physical properties, 367 technical data continuous filament yarns, 371 rovings, 369 textured yarns, 372 BD 200 rotor, 56, 62 BD 200 rotor spin box, 391 beam and truss model, 571 benzotriole, 272 Besfight, 355 beta-glucoronidase, 517 bi-directional barbs, 531 bicomponent yarns, 304 bioactive fibre, 284 biocompatibility, 454, 488 biodegradable polymers, 535 mineral origins, 551–9 natural origins, 536–7 biodegradable textile yarns, 534–65 applications, 560–5 biodegradable polymers, 535 electrospinning, 548–51 aligned nano-PLLA fibres, 549 PDLA/PLLA, 550 PLLA yarns in scaffolds, 550–1 fibres from mineral origins, 551–9 PGA-co-PLA fibres, 551–4 polyvinyl alcohol fibres, 554–7 fibres from natural origins, 536–7 chitosan and starch, 536 polylactic acid, 536–7 other fibres from natural sources, 557–9 abaca fibres, 558–9 alginate/chitosan fibre representation, 558
© Woodhead Publishing Limited, 2010
588
Index
alginate fibres, 557–8 pineapple fibres, 558 silk yarns, 559 PLA polymers spinning, 537–47 dry spinning method, 540, 544 fibre extrusion conditions and final properties, 538 melt spinning and drawing production outline, 539 melt spinning method, 537–40 PLLA speculative structure and degradation mechanism, 539 poly(hydroxybutyrate) fibre, 544–5 poly(p-dioxanone) fibres, 545–7 principles and importance of sustainable yarns, 534–5 twisted or cabled yarn hierarchical organisation, 563 biofouling, 486 biomaterials, 204, 487–8 Biopol, 564 bioreceptivity, 488 biosensing, 182–3 Body Fresh Yarn, 286 bonding, 500 bone cement, 480 bovine serum albumin, 518 Box–Behnken factorial design, 133 braided sutures, 527 braided thread, 8 braided yarn, 179, 399–400 characteristics, 8–9 production, 23–4 braiding, 23, 280 brocade, 280 BT 904 Rotona, 79 BT 904 rotor, 76–7 BT-30A method, 504 buildtech, 53 bulked continuous filament process, 88–9 bulkiness, 92 bulking, 91 modifying textile yarn structures, 92–100 bulked yarn production principles, 92–4 ring spun yarns, 94–6 yarns of different spinning technologies, 96–100 staple fibre yarn, 93 butanone, 466, 483, 484 butyl rubber, 155 structure, 156
cable yarn, 8 applications, 52–3 rope yarn, 52 tyre cord yarn, 52–3 characteristics, 8 production, 22 CAD see computer-aided design calcium stearate, 523 capacitive sensors, 238 capillarity, 526 carbon black, 444 carbon fibre fabrics, 315 carbon fibre threads, 508–9 carbon fibres and yarns, 345–60 applications, 357–9 aromatic sheets irregular stacking, 346 composition and structure, 345–6 fibre classification, 346 future trends, 359–60 properties, 347–57 cellulose-based carbon fibres, 348 compressive properties, 356 electrical properties, 355–6 functional properties, 357 Grayon carbon fibre weight loss vs temperature in air, 358 mechanical properties, 347–55 oxidised PAN and PAN-based carbon fibres thermal stability, 358 PAN-based carbon fibres, 349–52 pitch-based carbon fibres, 353–4 tensile properties, 355 thermal properties, 356–7 weight loss after ageing, 359 carbon filament fraction, 403 carbon nanofibre, 444 carbon nanotubes, 182 -coated conductive yarns, 180–2 bundles, 160 single walled and multi-walled, 161 structures, 160 technical textile yarns coating, 159–62 carding, 14, 186 cashmere, 204 yarn properties before and after engineering, 197 castor oil, 561 Catgut sutures, 514 cathodic arc deposition, 166–7 cellulose, 42 ceramic fibres and yarns, 360–5 applications, 365
© Woodhead Publishing Limited, 2010
Index commercial products, 365 ceramic rovings standards, 366 compositions, structures and properties, 360–5 alumina-based fibres properties and compositions, 364 non-oxide fibres, 360–2 oxide fibres, 362–5 silicon-based fibres properties and compositions, 361 future trends, 365 ceramic threads, 503–4 fibres of different chemical compositions properties, 503 chain scission, 454 charge-couple device, 238 chemical vapour deposition, 167, 308 chemo-mechanical fibrillation, 12 China fir sawdust, 561 chitin, 470 chitosan, 286, 463, 470, 473, 557 -coated yarns, 180 structure, 159 technical textile yarns coating, 158–9 chlorosulphonated polyethylene, 155–6 chromic acid salt, 516 chromic gut, 516 chromium trioxide, 516 citric acid, 473 citrus fibre, 209 classimat faults, 218–19 closed loop polyamide recycling process, 424 Cloth of Gold, 273 cloth tech, 50 CNT see carbon nanotubes co-extrusion, 176 co-ordinate system, 576 coating processes, 308–9 coatings, 140, 141 applications and properties of coated yarns adhesive-coated yarns for reinforcement, 177–8 chitosan-coated yarns, 180 extrusion-coated yarns, 178–9 ionomer-coated yarns, 177 packaging coated yarn products, 178 plasma-coated yarns, 180 polymer-coated staple fibre yarns, 179 PTFE-coated yarns, 177
589
SWNT-coated cotton yarn, 182 yarns coated with conductive substances, 180–2 coated yarns applications and properties, 176–82 methods and machinery, 170–6 air knife coating, 171 hot-melt coating, 174–5 impregnators, 173–4 knife coaters, 170 knife coating, 170 laminating, 176 Mayer rod/bad and coater, 172 roll coaters, 171–3 polymers, 144–62 acrylic ester, 148 acrylic polymers, 148–9 carbon nanotubes, 159–62 chitosan, 158–9 ethylene propylene monomer and some dienes, 153 ethylene vinyl acetate, 157–8 functional polymers and their uses, 145 nylon 6,6 and nylon 6, 157 nylons, 156–7 polyaniline, 149–50 polyesters, 157 polyisoprene, 151 polytetrafluoroethylene, 147–8 polyurethanes, 146–7 polyvinyl chloride, 145–6 polyvinylidene chloride, 146 rubber, 150–6 principles, 163–9 aqueous coating, 163–4 hot-melt coating, 164–5 metal coating, 165–9 polypyrrole and copper-coated paraamid fibre schematic, 166 solvent coating, 163 technical textile yarns, 140–83 formulations, 144 future trends, 182–3 textile coating and laminating, 141–4 uses of coated and laminated textiles, 142 coaxial transmission line method, 310 Cognetex FLC worsted ring frame, 135 cold plasma, 454 collagen sutures, 516 collagenase, 517 colour design system, 582
© Woodhead Publishing Limited, 2010
590
Index
COM4 value, 59 COM4 yarns, 59, 192 combed yarns, 115 combing, 186 ComforSpin process, 58–9 process schematic, 58 yarn formation, 57 comfort limit, 203 commercial-matrix composites, 365 commingled yarn, 6 production, 22–3 commingling, 389, 396–7 principle and commingled yarn structure, 397 compact spinning, 128–30, 191, 192–3 compact spun yarns, 61 hairiness different counts, 130 different twist levels, 130 complete benzylation treatment, 561 Composite Recycle Technology, 424 compression moulding, 405 computational fluid dynamics, 133 computer-aided design, 569, 572 system descriptions for yarn and fancy yarn structures, 579–83 Computer Aided Yarn, 252 condensed spinning see compact spinning conducting yarn, 24 conductive CNT yarns, 304–9 coating processes, 308–9 direct yarn spinning, 308 dye-printing system schematic diagram, 310 electro-spun fibre, 304–5 electrophoretic spun fibre, 305 experimental set-up used to make nanotubes ribbons, 306 melt spun fibre, 307 recondensed fibre, 305–6 simultaneously drawn and twisted yarn, 308 solution spun fibre, 306–7 spun continuous yarn from superaligned CNT arrays, 309 tabletop wet-spinning apparatus, 307 conductive textiles, 275 consolidation, 407 CF/PEEK composites consolidation quality, 411 main mechanisms, 408 quality evaluation, 410
Continuous Altex fibre, 363 continuous filament yarns being air-jet textured, 200 characteristics, 4–7 intermingled/commingled, 6 monofilament, 5 multifilament, 5–6 tape, 6–7 continuous suturing techniques, 526 contour figure, 204 contraction factor, 34 controlled fibrillation, 12–13 copper, 168 cord, 342 cord yarn construction, 48 Kevlar and polyester cords load– elongation curves, 48 properties, 47 core sheath yarn DREF-III yarn hollow structure, 103 twistless structure, 103 specific volume change after bulking, 98 tenacity change after bulking, 99 core spinning, 25–6, 52, 197–8 core spun thread, 497–8 core spun yarns, 6, 74, 197, 300 applications, 52 characteristics elastic core, 7 non-elastic core, 7 details, 78 production air-jet/vortex spinning, 80 elastic, 19–20 filament yarn, 19 friction spinning, 80 Lycra yarn, 20 ring spinning, 75–6 Rotona process, 79 rotor spinning, 76–7, 79 properties, 46–7 core yarn, 573 core yarn spinning, 74–80 core–cover ratio, 393 Coro Value Package, 66 Corobox SE 12 spinbox, 64–5, 66 Corolab, 253 Corolab 8, 66 Corolab ABS, 64 Corolab 8PP, 66
© Woodhead Publishing Limited, 2010
Index corona treatment, 475 cotton, 41–2 general properties, 501–2 spun thread, 497 steel-core threads, 506 sutures, 522–3 cotton silver, 391 count strength product, 217 cover spinning, 197–8 cover-spun yarn see wrap spun yarns crease recovery angle, 99 creep, 362 cross-section shape function, 578 crosshead extrusion, 175, 176 crosslinking, 454 cyanuric chloride, 486 Cyclic Tensile Abrader, 225, 226 CYROS, 249 Dacron, 157, 529 data fusion, 249–50 deviation rate, 245 Dexon, 516 Dexon II, 516 D-glass, 337 diameter scale function, 578 diaphragm forming process, 407 dichloromethane, 540 digital image processing, 234–5 basic concepts, 235–6 image data compression, 236 image modelling, 236 improving image quality and highlighting, 236 reinstating desired image features, 236 dimensional parameters, 26–32 linear density/count, 26–7 number of fibres/filaments in crosssection, 29 plied yarn linear density, 27 yarn diameter, 28 dimethyl sulphoxide, 554 diminishing slippage effect, 45 dip coating, 175 direct roll coating, 171–2 direct yarn spinning, 308 disperse dyes, 272 dodecylbenzene sulphonic acid, 304 Dornier 328 ribs, 421 Dornier 328 turboprop flaps, 421 drafting-against-untwisting process, 196 drag coefficient, 123
591
draw-textured thread, 498 drawing, 186 DREF, 67 DREF 1, 67 DREF 2, 56, 67–8 friction spinner, 68 yarns, 96, 97, 114 DREF 3, 67, 68, 300 friction spinner, 69 spinning machine, 102, 392 yarns, 96, 98 DREF 2000, 67, 69–70 friction spinner, 70 DREF 3000, 67, 70 DREF spinning, 391–3 spinning system and spun yarn, 392 DREF technology, 404 dry spinning method fibre extruder, 543 PLA polymers spinning, 540 DSM High Performance Fibers, 379 DuPont, 372 DuPont Type XV 100/86D, 403 dye-printing approach, 309 dynamic water vortex, 325 Dyneema fibre, 379, 380 Dyneema yarn, 381 e-glass, 330, 337 coated for twisted multifilament thread, 498 e-textiles, 181, 275, 292 eccentricity index, 250 ECR glass fibres-5, 344 effect yarn, 573 Egyptian cotton, 205 elastic elongation, 41 elastic yarn, 19–20 elasticity, 525 electrical conductivity, 275–6 electro-conductive textile yarns, 298–326 applications, 313–16 anti-electrostatic, 315 antibacterial, 315 electrical energy and data transportation, 314 electromagnetic shielding, 315 textile electrodes and sensors, 314 thermal purposes, 316 wireless communication, 313 conductive yarns production, 300–3 friction-spinning, 300 hollow-spinning, 302–3
© Woodhead Publishing Limited, 2010
592
Index
ring-spinning, 301–2 electro-spun nanofibre yarn, 325 formation method, 326 future trends, 316–26 direct conductive electro-spun SNT composite yarn formation, 325–6 rotational magnetic field aided false twisting of metallic filaments, 319–23 rotational magnetic field aided interlacing of metallic filaments, 316–19 manufacture and structure, 299–309 bicomponent yarns, 304 conductive CNT yarns, 304–9 inherently conductive polymer, 303–4 yarns with metallic fibres or filaments, 299–303 measurements, 309–13 electromagnetic shielding effectiveness, 309–12 electrostatic discharge, 312–13 metal filament fed from the sides of front roller, 302 fed in the middle of front roller, 302 feeding angle, 301 roving core spun yarn spinning mechanism, 301 uncommingled conductive yarn structure, 303 electro-spun fibre, 304–5 electrodeposition, 167 electroless deposition, 168 electroless plating, 168 electroluminescent yarns, 265–6 schematic diagram, 266 electromagnetic shielding, 276, 315 ASTM 4935, 310 specimen dimension for reference and load test, 311 testing apparatus set-up, 311 effectiveness, 309–12 ASTM ES7, 311–12 electronic smart textiles, 181 electronic textiles see e-textiles Electronic Vacuum Adjustment system, 66 electrophoretic spun fibre, 305 electroplating, 167 electrospinning, 242, 243, 304, 325, 548–51 experimental set-up device, 548
nine simultaneous positive needles simulation, Plate I electrostatic discharge, 312–13, 315 generator and discharge tip for contact method, 314 EliTe spinning, 57, 59–60 schematic, 59 emeraldine, 149–50 entangling see commingling erythemal spectral effectiveness, 269 ethanol, 536 Ethibond, 518, 521 Ethilon, 518 ethyl orthosilicate, 556 ethylene propylene diene monomer, 153–4 ethylene propylene rubber, 153–4 ethylene vinyl acetate reinforced adhesives, 178 structure, 158 technical textile yarns coating, 157–8 ethylenediamine, 459 evaporation, 166 expanded rubber, 158 EXPERT, 249 extrusion-coated yarns, 178–9 braid yarns, 179 PVC-coated yarns, 179 vinyl-coated fibreglass yarns, 179 extrusion coating, 164, 174–5 extrusion laminating, 174–5, 176 false-twist textured yarns, 241 false-twist texturised PLLA yarn, 562 false twist texturising, 86 developments, 86–7 fancy yarns, 200 CAD system description for yarn and fancy yarn structures, 579–83 CAD generated yarn and fancy yarn structure, 580 computer generated yarn structures with real yarn samples, 580 yarn CAD system overview, 583 yarn simulation parameters, 581 structures mathematical modelling, 573–9 3D mathematical descriptions, 574–7 structure irregularities modelling, 577–9 yarn design using 3D computer graphics and visualisation techniques, 568–84
© Woodhead Publishing Limited, 2010
Index cloths and yarns, 570–2 microstructures, 573 FancyControl, 65 FancyLink, 65 Fancynation, 65–6 Fancynator, 198 FancyOasis Gold, 65 FancyPilot, 65 FancyProfile, 65 fasciated yarns, 70 Fashionator, 198 fatigue failure, 224 fatigue strength, 220 ferrous sulphate, 465, 483, 484 fibre assembly, 62–3 blending, 280 diameter, 187 distribution, 202 fineness, 114 individualisation, 62 length, 113, 188 modification, 188–9 packing coefficient, 91 parameters, 37–9 bending rigidity, 38–9 fibre diameter, 37–8 length, 39 specific surface area, 38 torsional rigidity, 39 properties, 40 torsion, 34 fibre–matrix bond, 409 fibrillated tape yarn, 6, 12 fibrillation, 44 by transverse forces, 12 ratio, 13 technique, 13 fibrin, 560 filament angle, 36–7 filament peeling resistance, 229 filament winding, 405–6 filament wrapping, 17 film stacking technique, 562 finer and softer textile yarns engineering, 185–209 applications, 204–5 importance, 185–6 properties, 203–4 engineering methods, 186–201 air-jet textured continuous filament yarn, 200 air-jet texturising, 199–201
593
cashmere properties before and after engineering, 197 fibre to yarn conversion systems, 189–99 JetRing spinning system schematic diagram, 193 Sirospun process, 190 solo and compact spinning principles, 192 future trends, 205–9 bamboo, 205 microfibre yarns, 205–9 polyester microfibre yarn properties, 206 standard pie wedge fibre, 209 raw material requirements for engineering, 187–9 fibre diameter, 187 fibre diameter and crimp selection, 188 fibre length, 188 fibre modification, 188–9 hauteur on yarn evenness and spinning performance, 188 structure, 201–3 conventional ring spun yarn vs JetRing spun yarn, 201 fibre distribution and packing density, 202 number of fibres in the yarn crosssection, 202–3 flat tape yarn, 11–12 flax, 185, 423–4 Flexon sutures, 523 flexural rigidity, 38, 113 fluorescent yarns, 261, 262 fluoroelastomers, 154 Fluorofil, 518 Flying Laser Spot Scanning System, 245 foam generator, 144 foam rubber, 158 Fokker 60, 421 folded yarn, 8 characteristics, 8 production, 20–2 cable yarn, 22 plied yarn, 20–2 Fresnel diffraction principle, 245 Fresnel Zone Plate technique, 545 friction spinning, 15–17, 56, 67–70, 300 core spun yarns production, 80 latest developments, 69–70 DREF 2000, 69–70
© Woodhead Publishing Limited, 2010
594
Index
DREF 3000, 70 method, 416 operation principle, 67–9 friction spun yarns, 84, 92, 102 technical applications, 85 Fukurami, 203 fully drawn yarn, 88 G 567 Yarn Hairiness Tester, 243 gassing, 500 geogrids, 277 geometric torsion, 34 geotextiles, 53, 276, 511 GF/PTFE commingled yarns, 396–7 GF–PP commingled Twintex yarns, 402 glass, 502 glass fibres and yarns, 330–45 applications, 344 nomenclature and specific applications, 332 commercial products, 338–44 cabled yarns, 342, 344 composition ranges, 331 continuous filament yarns, 339, 342 folded yarns, 342 glass rovings package dimensions, 341 product consolidation steps, 338 rovings, 338–9 single, folded and cabled yarns schematic diagrams, 339 textured yarns, 342 composition and structure, 330 designation and technical data cabled yarns, 345 continuous filament yarns, 341 folded yarns, 344 rovings, 340 textured yarns, 343 future trends, 344–5 glass networks schematic diagram, 333 properties, 330–8 chemical properties, 335 chemical resistance, 333, 337 electrical properties, 335, 337 physical properties, 330–3, 334 tensile strength after corrosion, 337 thermal properties, 336, 337–8 glass threads, 505–6 glass transition temperature, 432 glazing, 500 global co-ordinate system, 576
glow-in-the-dark yarns see electroluminescent yarns glutaraldehyde, 564 glycerol, 564 Goal 1210, 86–7 contact heater, 87 easy threading, 86 false-twist motor spindle, 87 improved thread path with ergonomic creel, 86 package build, 87 setting zone, 87 straight yarn path system, 87 gold, 168, 278 GraphicDesigner, 65 graphite, 346 graphite sheets, 346 gravure coating, 173, 174 Grayon fibres, 356 GT-15, 506 GT-23, 506 GT rotors, 66 Gutermann’s monocord sewing thread, 510 Halar, 500 Hari, 203 Heavy Weight Package, 66 Heltra process, 389, 397 stretch broken yarn, 398 Hevea brasiliensis, 151 Hi-Nicalon fibres, 362 Hi-Nicalon fibres Type-S, 362 high modulus high tenacity fibres and yarns, 329–82 aramid fibres and yarns, 370–7 applications, 377 commercial products, 375–7 composition and structure, 370, 372–3 future trends, 377 properties, 373–5 basalt fibres and yarns, 365–70 applications, 370 commercial products, 368–70 composition and structure, 365, 367 future trends, 370 properties, 367–8 carbon fibres and yarns, 345–60 applications, 357–9 composition and structure, 345–6 future trends, 359–60 properties, 347–57 ceramic fibres and yarns, 360–5
© Woodhead Publishing Limited, 2010
Index
applications, 365 commercial products, 365 compositions, structures and properties, 360–5 future trends, 365 fibre classification, 329 glass fibres and yarns, 330–45 applications, 344 commercial products, 338–44 composition and structure, 330 future trends, 344–5 properties, 330–8 high-performance polyethylene fibres and yarns, 378–82 applications, 381 commercial products, 381 composition and structure, 378–9 future trends, 382 properties, 379–81 high modulus polyethylene, 502 high-performance polyethylene fibres and yarns, 378–82 applications, 381, 382 commercial HPPE fibres mechanical properties, 380 transverse properties, 380 commercial products, 381 composition and structure, 378–9 HPE and normal PE macromolecular orientation, 379 UHMWPE, 378 future trends, 382 properties, 379–81 chemical resistance, 380 electrical properties, 381 physical properties, 379–80 thermal properties, 381 Hoechst PEEKM, 403 hollow-spindle spinning see wrap spinning hollow-spinning, 302–3 schematic diagram, 303 hollow yarns, 102–9 air permeability, 107 core-sheath type DREF-III yarn, 103 fabric properties, 105–9 mechanical properties, 106 production principles, 102–5 stress-strain behaviour, 104 thermal resistance, 108 water absorbency, 109 yarn properties, 104–5 homopolymerisation, 465, 483 Hostaphana, 278
595
hot-melt coating, 164–5, 174–5 crosshead extrusion, 175 extrusion coating/laminating, 174–5 hot press technique, 405, 563 hybrid yarns, 387–426 benefits, 401 characterisation, 400–4 effect of raw materials properties, 401 fibre distribution, 404 friction, flexibility and compressive properties, 400–1 performing behaviour, 403 process parameters, 402 reinforcing fibres damage during manufacture, 403–4 structure and properties, 400 compaction and consolidation, 407–13 CF/PEEK composites consolidation quality, 411 consolidation quality, 410–11 consolidation quality evaluation, 410 fibre–matrix adhesion, 409–10 composite property relations, 413–20 fibre distribution, 415–16 polished areas made with different hybrid yarns, 414 voids and their distribution, 414–15 mechanical properties, 416–20 fatigue and interlaminar fracture, 419–20 impact properties, 418–19 tensile properties, 416–18 micro-braided yarn structure, 399 moulding parameters on microstructure and mechanical properties, 412–13 compaction time, 412 effect of pressure, 413 tool temperature, 413 relative strength and yarn count dependence on air pressure and nozzle type, 404 thermoplastic composites manufacture, 405–7 autoclave moulding, 406–7 bladder inflation moulding steps, 407 compression moulding, 405 filament winding, 405–6 inflation moulding technique, 407 pultrusion process, 406
© Woodhead Publishing Limited, 2010
596
Index
thermoplastic composites potential application areas, 421–2 aircraft applications, 421 industrial applications, 421–2 trends in thermoplastic composite applications, 422–5 car hatrack manufactured from recycled thermoplastic composite, 426 environmental issues and recyclability, 424–5 natural fibre reinforced thermoplastic composites, 422–4 types, 389–400 air-jet texturing, 393–6 braided yarn, 399–400 commingling, 396–7 DREF spinning, 391–3 Kemafil technology, 399 parallel winding, 397 ring spinning, 390–1 rotor spinning, 391 Schappe technology, 399 stretch breaking, 397–9 wrap spinning, 393 hypalon, 155–6 IA-3, 72 image analysis, 232 image data compression, 236 image modelling, 236 image processing, 232 IMAQ Vision, 251 immersion coating, 175 impregnated strand method, 355 impregnators, 173–4 in situ microencapsulation, 556 in vitro hydrolysis test, 562 industrial fabrics, 216 industrial sewing threads, 495–512 airbags threads, 510 antistatic safety workwear threads, 511 application categories, 495–6 automotive and supply industries, 495 filtration, 496 geotextiles, 496 leather goods, 496 multi-needle stitching, 496 other applications, 496 protection, 496 sun protection, 495 aramid threads, 506–7
automated multi-directional sewing threads, 502 carbon fibre threads, 508–9 fabrics and threads sizes, 501 fibres for sewing of airbags, 510 finishing, 500 general properties of fibres used for sewing threads, 501–2 cotton, 501–2 glass, 502 high modulus polyethylene, 502 meta aramid, 502 nylon, 502 para aramid, 502 polyester, 502 polypropylene, 502 steel, 502 viscose, 502 geotextiles threads, 511 numbering and packaging, 500–1 outdoor applications, 509–10 PTFE fibre thread, 507–8 rocks chemical composition suitable for basalt fibre production, 505 sewing threads outdoors strength retention, 510 structure, 496–9 air-entangled thread, 499 air-jet textured thread, 499 core-spun thread, 497–8 draw-textured thread, 498 monocord thread, 498 monofilament thread, 499 spun thread, 497 tape thread, 499 twisted multifilament thread, 498 ultra high modulus polyethylene threads, 508 various sewing threads in nonmedical technical applications, 511 very high temperature applications, 502–6 ceramic threads, 503–4 glass threads, 505–6 silica fibre threads, 504–5 steel-core threads, 506 indutech, 49–50, 53 inflation moulding technique, 407 inherently conductive polymer, 303–4 integrated humidity sensing, 309 intelligent apparel see smart apparel intelligent textiles see smart textiles interlacing see commingling
© Woodhead Publishing Limited, 2010
Index interlacing braiding techniques, 344 intermingled yarn, 6 production, 22–3 intermingling see commingling ionomer-coated yarns, 177 IQ Clean, 77, 78 ISO-10993, 528 itch point, 203 jet-ring spinning system, 131–2 effect of air pressure on yarn hairiness, 132 jet-winding system, 132–5 JetRing process, 193–4 JetWind Plus process, 195–7 air nozzle, 196 drafting-against-untwisting concept, 195 JetWind process, 194–5 experiment layout, 195 JIS-R-7601, 355 jute, 423 jute-yarn–Biopol composites, 563 Kapton tape, 545 Kawabata’s Evaluation System, 203 Keisokki KET-80, 245 Kemafil technology, 399 Kemafil yarn, 398, 404 kenaf fibre, 561 Kevlar, 48, 372, 375, 418 aramid threads, 506 geotextiles, 511 spun thread, 497 steel-core threads, 506 twisted multifilament thread, 498 Kevlar 29, 373, 376 Kevlar 49, 376 Kevlar 149, 373, 376 Kishimi, 203 kiss coating, 172–3 knife coaters, 170 knife on air systems, 170 knife over roller coating systems, 170 knife over rubber blanket method, 170 knife over table coating system, 170 knitting, 123–4 knot-pull strength, 524 knot security, 525 knot tie down, 525 knottability, 526 Koshi, 203 KS 200, 62
597
Kuralon K-II, 554 lacteal spinning dopes, 556 lamés, 280 laminate, 140 laminating, 141, 176, 277–8 lamination, 140, 169 laser ablation, 167 Laserspot, 245 latex, 151 laundering, 281 Lawson Hemphill YPT, 238 lazy shirt, 288 LD nozzle, 402 Ledal Spa, 263 Leica MZ6, 114 leucoemeraldine, 149–50 levonorgestrel, 561 linear aliphatic polyamides see nylon linear density, 26–7 units, 27 linen sutures, 522 lipase PS, 559 loosening, 186 low oriented yarn, 88 low pressure chemical vapour deposition, 166 LOX-E, 362 LOX-M, 362 lubrication, 500 luminescent yarns, 261–2 luminous yarns, 261 Lurex polyester, 274 Lycra, 80 Lycra yarn, 20 lysine-based diisocyanate, 559 magnetic rotor positioning system, 66–7 main winding, 319 manila hemp, 558–9 MasterSpinner, 67 Maxon, 517 Mayer rod, 171, 172 mechanical vapour compression process, 422 Medical Device Amendment, 515 medical textiles, 204 medical yarns, 183 meditech, 50 melt spinning, 10, 24 PLA polymers, 537–40 shape memory polymer yarns manufacture, 435
© Woodhead Publishing Limited, 2010
598
Index
melt spun fibre, 307 mercerising, 500 meta aramid fibres, 373 general properties, 502 metal coating, 165–9 conductive yarns, 180 electroless plating/deposition, 168 electroplating/electrodeposition, 167 lamination, 169 plasma treatment, 168–9 plating, 167 vacuum coating, 166–7 with a binder, 165 metallic composite yarns manufacture, 279–80 braid, 280 core-spun yarns, 279 fibre blending, 280 wrapped yarns, 279–80 metallic fibres, 273, 274–5 forms, 278–9 supported, 278–9 unsupported, 278 properties, 275–6 electrical conductivity, 275–6 electromagnetic shielding, 276 heat resistance with superior mechanical properties, 276–7 structure, 275 metallic yarns, 273–82 metallised thread, 498 metallising, 278 metalloplastic, 274 metalloplastic yarns, 273–82 metering rod coater, 171 methacrylic acid, 462 methanol, 466, 483 methylene chloride, 548 micro-denier yarns, 229–30 micro-electromechanical systems, 443 micro-fibres, 229 micro-machining techniques, 531 microbond technique, 558 microfibre yarns, 205–9 Milaine Thunderon SP, 511 MJS 801, 70 MMA-g-UHMWPE grafted fibre, 480 modelling module, 581 modified Hohenstein test, 473 moisture vapour permeability, 102 transmission, 96
transmission rate, 96 monocord thread, 498 monofilament thread, 499 monofilament yarn, 5, 6 applications, 49–50 products, 51 properties, 43–4 mullite, 365 multi-walled nanotubes, 159, 161, 444 multifilament yarn, 5–6, 6 applications, 50 products, 51 properties, 44 multiple yarn diameter measurement, 250 Multitester, 237 Murata Jet Spinner, 57, 70–1 principle, 71 vs Murata Vortex Spinning, 74 Murata Twin Spinning, 72 Murata Vortex Spinning, 57, 72, 198 vs Murata Jet Spinning, 74 MVS 851, 73 MVS 861, 73 MWNT see multi-walled nanotubes Mylar, 278 N-halamines, 472 Nafion, 181 nano-finishing, 273 nano-silver, 286 Nano-Tex, 162 nanomaterials, 242 nanotechnology, 242 natural fibres, 186 natural rubber, 150–1 needle attachment force, 525 needle roller fibrillation, 12–13 neem leaf extract, 473 neoprene, 152–3 Nextel, 363 Nextel 312, 503, 504 Nextel 440, 503, 504 Nextel 312 fibre, 363 Nextel 610 fibre, 363 Nicalon, 360 nickel, 168 nickel-titanium, 288 Niho Sanmo dyeing company, 511 nips, 241, 242 nitrile rubber, 155 NL-200, 362 N,N-dimethylformamide, 305, 435, 437, 548
© Woodhead Publishing Limited, 2010
Index Nomex, 42, 372, 375 aramid threads, 506 spun thread, 497 steel-core threads, 506 twisted multifilament thread, 498 non-absorbable sutures, 528 list of examples, 519 normal average method, 582 novel technical textile yarns, 259–92 antimicrobial yarns, 282–7 antimicrobial fibre/yarns, 284–5 durable fibre/yarn production methods, 285–6 ideal characteristics, 284 microbes effect on consumers and textiles, 282 physical incorporation into fibre, 285 substances used, 286–7 textile antimicrobial treatment, 283 textiles fabrication, 283–4 future trends, 292 metallic and metalloplastic yarns, 273–82 applications in technical textiles, 281 care of fabrics, 281 fibre structure, 275 fibre/yarn properties, 275–7 fibres forms, 278–9 manufacturing composite yarns, 279–80 manufacturing processes, 277–8 metallic fibres or yarns, 274–5 producers, 281–2 rotor twister sketch, 279 sintered metal fibre felt, 277 uses, 280–1 reflective yarns, 259–66 classification, 261–6 ultraviolet protected yarns, 266–73 factors affecting UPF of apparel textiles, 271 preparation, 271–3 recommendations concerning clothing for photosensitivity patients, 271 standard UPF for UV protective clothing, 269 sun protection factor, 267–8 technological options to apply UV absorbers, 273 textile qualities and UV production, 269–70
599
ultraviolet protection factor, 268–9 UPF textile classification, 270 yarns for specific purposes, 287–92 anti-stress yarn, 290 antiallergic yarn, 291 antistatic yarn, 289–90 auxetic yarns, 287–8 shape-memory yarn, 288–9 soluble yarn, 291–2 nozzle winding system, 132–5 Numeri, 203 Nurolon, 518 nylon, 10, 42, 498 general properties, 502 melt spun fibre, 307 sutures, 518 technical textile yarns coating, 156–7 Nylon 6,6, 375 O/C atomic ratio, 460 OASYS, 243, 244, 249 obliquity effect, 45 O2–CF4 treatment, 479 Ocimum sanctum, 287 olivine, 365 open-end friction core-spun yarns, 300 open-end rotor spun yarns, 197 optical filtering, 239 optical sensors, 238 optical signal processing, 241 Optim, 188 Optim Fine, 189 Optim Max, 189 Optim Wool Fibre Processing Machine, 189 organoclay, 444 package, 186 packagetech, 53 packing density, 202 pad–dry–cure process, 437 para aramid, 375 fibres, 373 general properties, 502 paradioxanone, 517 Parafil 1000, 82 Parafil 2000, 82 Parafil spinning, 82 Parafil wrap spinning, 81 parallel winding, 397 side-by-side yarns structures, 398 parallel yarns see wrap spun yarns partially oriented yarn, 88 PBAG6000-based polyurethane, 446
© Woodhead Publishing Limited, 2010
600
Index
PDLA see poly-DL-lactide PEEK see poly ether ether ketone pernigraniline, 149–50 PET see polyethylene terephthalate PHAG5000-based shape memory polyurethane, 446 phase change materials, 437, 556 phenyl benzotriazole, 272 Phong’s illumination model, 581 phosphorescent yarns, 262–3 photo-luminescent yarns, 263–5 phthalocyanine-dyed yarn, 291 physical vapour deposition, 166 pie wedge fibre, 209 pilling, 124 pineapple fibres, 558 PLA see poly(lactic acid) plagioclase, 365 plain gut, 516 plane-wave electromagnetic field, 310 plasma, 454, 456–7 immobilisation, 477–9 sterilisation, 476–7 technology, 453–4 plasma assisted chemical vapour deposition, 166 plasma enhanced chemical vapour deposition, 166 plasma-treated yarns, 180 biomedical applications, 452–88, 468–87 absorption percentage vs time of exposure, 474 antimicrobial treatment, 470, 472–6 bone cement, 480 cotton fabric treated with air plasma and antimicrobial finish, 474 fibre content on tensile properties, 480 microwave-induced argon plasma treatment on silk fabrics, 477 P. aeruginosa in silk fabrics before and after microwave-induced argon plasma treatment, 478 plasma immobilisation, 477–9 plasma sterilisation, 476–7 shaking speed effect on bacteria growth inhibition in flask, 471 stem cells attached onto polyester fabric, 486 sutures, 480–4 tissue engineering, 484–7 unspecific protein adsorption
minimisation, 487 wound dressings, 469–70 zone of bacteriostasis, 475 fabrics ultimate tensile strength change according to plasma treatment time, 479 medical textile market in India, 453 metastable atoms properties, 456 O/C atomic ratio evolution, 460 PET textile samples rms surface roughness and surface area data, 461 plasma active species action in polymers mean depth, 455 plasma processing chemistry, 457–68 activation, 457–61 grafting, 461–7 polymerisation, 467–8 plasma treatment, 168–9, 287 amine functionalities TFBA derivatisation reaction scheme, 459 chemistry, 457–68 activation, 457–61 grafting, 461–7 polymerisation, 467–8 contact angle variation with degree of grafting under different additives, 484 degree of grafting variation homopolymerisation variation with ferrous sulphate concentration, 465 monomer concentration, 482 reaction time for different plasma treatment times, 482 water-organic composition, 466 experimental conditions effect on immobilised ALP activity, 479 gases and their applications, 458 grafting process under different reaction conditions, 485 homopolymer yield at different monomer concentrations, 483 reaction temperature influence on degree of grafting, 463 yarns for biomedical applications, 452–88 antimicrobial treatment, 470, 472–6 bone cement, 480 plasma immobilisation, 477–9 plasma sterilisation, 476–7 sutures, 480–4
© Woodhead Publishing Limited, 2010
Index tissue engineering, 484–7 wound dressings, 469–70 plasma–polymer interaction, 454–5 plasticity, 525 Plastolon thread, 507–8 Plastomer Technologies, 508 plating, 167 Platt type 888, 199 plied yarns, 8, 342, 573 applications, 52–3 characteristics, 8 geometry, 35–7 filament angle, 36–7 twist introduced in the plying process, 35–6 linear density, 27 production ring twister/down-twister, 20–1 two-for-one twister, 22 up-twister, 21–2 up twister and two-for-one twister, 21 properties, 47 PLLA see poly-L-lactide ply cord, 8 pneumatic texturing, 401 Polarity Test Therapy machine, 290 Poloxamer 188, 523 poly-DL-lactide, 537, 550 poly ether ether ketone, 498 poly(3-hydroxybutyrate), 536, 544 mechanical properties variation with draw ratio, 545 poly(3-hydroxybutyrate-co-3hydroxyvalerate), 458, 558–9 poly-L-lactide, 537, 561, 562 aligned and random fibres, 549 as-spun fibres tensile properties, 541 DSC scans of as-received yarns, 560 hot-drawn fibres tensile properties, 542 melting endotherms, 543 speculative structure and degradation mechanism, 539 yarns in scaffolds, 550 poly(acrylic acid), 463, 473, 555 polyacrylonitrile grafts, 481 polyaluminocarbosilane precursor, 362 polyamide, 42, 44, 475 reinforced adhesives, 178 polyamide 66, 510 polyamide nylon, 156 polyaniline, 303–4 main structures, 149
601
technical textile yarns coating, 149–50 polybutylene, 521 poly(butylene succinate), 559 Polycarbon, 347 polychloroprene rubber, 152–3 structure, 152 polycondensation, 556 polydioxanone, 516, 517 poly(e-caprolactone), 548 polyester, 10, 25, 42, 44, 94, 270, 272, 475 airbag threads, 510 cords, 48 filament, 391 general properties, 502 microfibre yarn, 206 reinforced adhesives, 178 spun thread, 497 technical textile yarns coating, 157 polyester–cotton blends, 497 polyethylene glycol, 486 polyethylene terephthalate, 459, 462, 470, 486 chitosan grafted PET formation, 471 melt spun fibre, 307 monofilaments roughness RMS values, 464 rms surface roughness and surface area data, 461 structure, 157 surface modified PET bacteria growth inhibition, 472 virgin, acrylic acid grafted and chitosan immobilised monofilaments, 464 polyglactin, 516 Polyglactine 910, 517 poly(glycolic acid), 516, 550, 560 fibres, 453 sutures, 530 poly(glycolide-co-lactide), 551–4 monofilament SEM results, 553 morphological changes, 552 surface morphology change with in vitro time, 553 polyglyconate, 517 poly(hydroxyethyl methacrylate), 486 polyisoprene, 151 poly(lactic acid), 453, 559 polylactic acid resin, 561 polylactide, 536–7 polymer-coated staple fibre yarns, 179 polymethyl methacrylate, 307 poly(p-dioxanone), 545 fibre microfailure modes, 547
© Woodhead Publishing Limited, 2010
602
Index
mechanical properties with elapsing hydrolysis time, 546 surface cracks, 546 polypeptide growth factors, 487 polyphenylene sulphide, 397 polypropylene, 10, 42, 44, 459, 481 clearing system, 66 general properties, 502 monofilament sutures, 530 suture, 518–19 twisted multifilament thread, 498 polysaccharides, 470 polytetrafluoroethylene -coated Kevlar, 177 -coated quartz, 177 -coated yarns, 177 coated fibreglass yarns, 177 coated for twisted multifilament thread, 498 fibre thread, 507–8 technical textile yarns coating, 147–8 thread finishing, 500 polyurethane, 80 finishes, 500 structure, 147 technical textile yarns coating, 146–7 polyvinyl alcohol, 24–5, 100, 554–7 stress-strain curves, 555 polyvinyl chloride -coated yarns, 179 technical textile yarns coating, 145–6 polyvinyl fluoride, 148 polyvinylidene chloride, 146 polyvinylidene fluoride, 148 Poval, 554 PrimaLoft, 208 prismatico yarns configuration, 263 parameters and photos, 264 producer’s twist, 5 Prolene, 518, 519 proteinase K, 559 pseudo-monofilaments, 515 PTFE see polytetrafluoroethylene pultrusion process, 406 purine, 477 PVC see polyvinyl chloride pyrimidine, 477 pyroxene, 365 quaternary ammonium salts, 472 QuickDesigner, 65 R 40 rotor spinner, 67
radio frequency plasma treatment, 454, 459 radiometric UV transmission tests, 268 Raman mapping, 459 Rasant, 509 Rastex, 507 Rayleigh wave phonon, 356 recombinant DNA technology, 531 recondensed fibre, 305–6 recondensing method, 305 recovery stress, 434 reflective yarns, 259–66 classification, 261–6 electroluminescent yarns, 265–6 luminescent yarns, 261–2 phosphorescent yarns, 262–3 prismatico yarns, 263 retro-reflective or photoluminescent yarns, 263–5 reflective material day/night contrast, 260 Repco, 199 retraction factor, 34 retro-reflective yarns, 263–5 before/on reflection, 264 glass beads principle, 265 ion of incoming light, 264 manufacturing process, 265 Retroglo, 265 Reutlinger Web Tester, 225 reverse roll coating, 173, 174 Rieter ComforSpin K 40, 129 Rieter K44, 202 rigid yarn, 18–19 ring spinning, 15, 56, 301–2, 390–1 core spun yarns production, 75–6 modified yarn path, 135–6 yarn formation, 57 ring spun yarns, 57, 110 bulking, 94–6 fabric characteristics, 95–6 yarn characteristics, 95 hairiness, 125 different counts, 130 different twist levels, 130 prediction performance of ANN and regression models, 128 RJS 804, 72 ROBOfeed, 67 RoCoS compact spinning, 57, 60–1 schematic, 61 roll coaters, 171–3 direct roll coating, 171–2 gravure coating, 173
© Woodhead Publishing Limited, 2010
Index kiss coating, 172–3 metering rod coater, 171 reverse roll coating, 173 Roller Jet Spinner, 72 rope, 342 rope yarn, 52 rotational magnetic field false twisting of metallic filaments, 319–23 electromagnetic field frequency on filament twisting, 324 false twisted current-carrying metallic filaments, 323 false twisting zone schematic diagram, 320 filament current vs interlacing points number, 324 filament twist formation, 324 laboratory set-up, 322 magnetic forces induced on each filament in the twisting box, 323 run capacitor single-phase induction motor schematic diagram, 320 single-phase run capacitor induction motor properties, 321 interlacing of metallic filaments, 316–19 conductive filaments properties, 318 interlaced two conductive filaments, 318 laboratory set-up, 317 magnetic field rotational speed effect on interlaces per centimetre, 318 Nd–Fe–B magnets properties, 317 Rotofil, 71 Rotona, 76 core spun yarn, 79 process, 79 rotor spinning, 15, 16, 61–7, 114, 391 core spun yarns production, 76–7, 79 latest developments, 63–7 adjustable BYPASS, 63 Corobox SE 12 spinbox, 64–5 Corolab ABS, 64 Coropack, 66 DREF 2 friction spinner, 68 DREF 3 friction spinner, 69 Fancynation, 65–6 magnetic rotor positioning system, 66–7 polypropylene clearing system, 66 SC 1-M and SC 2-M spinboxes benefits, 65
603
Speedpass, 64 Torque-Stop, 64 operation principle, 61–3, 62 fibre assembly, 62–3 fibre individualisation, 62 principle of operation resultant yarn withdrawal, 63 twist insertion, 63 rotor twister, 279–80 Rotorcraft Compact Spinning System, 60 roving, 18, 186 rubber, 150–6 see also specific types S-twist, 31 SC see silicon carbide scaling factor, 577 Schappe technology, 399, 416, 508 Schappe yarn, 398, 404, 416 Scotchlite reflective yarns, 261 SE 8 spin box, 63 SE 9 spin box, 63 self-twist spinning, 199 sericin, 529 SERVOcan, 67 SERVOcone, 67 shading model, 582 shape fixity, 434 shape-memory alloy fibres, 288 shape memory polymer yarns, 288–9, 429–48 advantages over shape memory alloys, 434 applications, 437–44 breathability, clothing comfort, wrinkle recovery, 437–8 engineering fabric aesthetics, 438–40 further applications, 443–4 medical field, 440–3 bending modulus vs temperature, 447 composite loosely woven fabric shape memory recovery flexible yarn, 441 samples with varied fabric design, 442 SMP yarn, 439 fibre cross-section, 448 future trends, 444–7 hybrid combined with non-SMP, 446–7 nanocomposite with nano reinforcement phase, 444–5 manufacture, 434–7
© Woodhead Publishing Limited, 2010
604
Index
melt spinning, 435 SME transfer to genetic fibre after finishing process, 436–7 wet spinning, 435–6 medical possibilities, 442 SMP fibres with different MWNT contents shape recovery stress, 445 string-like material recovery to a tubular device, 442 thermo-mechanical behaviour, 431–4 AB-polymer network macroscopic shape memory effect, 432 elastic modulus variation with temperature, 433 typical behaviour, 433 shape-memory textiles, 288 shape recovery ratio, 434 shape scale function, 578 Shari, 203 shed, 225 Shinayakasa, 203 Shirley yarn hairiness tester, 117, 118 silica fibre threads, 504–5 silicon carbide, 444 silicone rubber, 151–2 structure, 151 silk sutures, 522, 529–30 silk yarns, 559 silver, 168, 169, 183, 291 silver carboxylate, 473 silver-coated fibre fabrics, 315 Silver Transfer Film, 261 Simplext-P radiopaque bone cement, 480 Single Drive Sliver Intake, 64 single-phase induction motor, 319 single-walled nanotubes, 159, 161, 305, 554 single yarn, 573 elongation, 217–18 strength, 217 SIRO spinning, 20 Sirospun, 190–1 attachment in place, 191 worsted ring spinning machine process, 190 sisal fibre, 423 sizing, 217, 219, 228 skin friction coefficient, 122 skin sensorial wear comfort, 185–6 slicing, 13 sliding knots, 525 sliver, 14
smart apparel, 298 smart fibres, 204 smart properties, 292 smart textiles, 275, 292 smart yarn, 181 Smartcel, 158 sodium alginate, 557 soft finish, 500 solar spectral irradiance, 269 Solar Thread, 508 Solospinning, 191–2 soluble yarn, 291–2 solution spinning process, 306 solution spun fibre, 306–7 solvent coating, 163 soy protein isolate, 564 spandex, 53 spectoradiometers, 268 Spectra, 379, 380, 381 twisted multifilament thread, 498 ultra high modulus polyethylene threads, 508 spectrophotometers, 268–9 Speedpass, 64 spin-draw process, 537 spinning, 114–15, 186 effect of yarn hairiness, 122 process steps, 14 spinning triangle, 57, 129 splittable fibres, 208 sporttech, 50 spring-mass model, 570 spun thread, 497 spun-twist texturised PLLA yarn, 562 spun yarn, 6, 186 properties, 44–5 technology, 25 sputtering, 166 square knots, 525 stainless steel fibres, 280 Standards Australia Committee TX/21, 269 staple fibre yarns, 91 bulking process, 93 polymer coated, 179 staple fibres, 186 staple spinning system, 202–3 staple yarns characteristics, 7 production, 13–17 filament wrapping, 17 twisting by ring spinning machine, 14–15
© Woodhead Publishing Limited, 2010
Index
twisting by rotor and friction spinning machine, 15–17 steel, 502 steel-core threads, 506 strain fixity rate, 431 stretch breaking, 397–9 strip-back, 390 styrene-butadiene rubber, 154–5 structure, 154 sub grade soil, 511 Suessen Elite, 129, 130, 192, 202 sun protection factor, 267–8 Super Spectron, 72 supersonic air-jet, 499 surgical threads, 495, 513–32 characterisation, 524–30 biological characteristics, 527–30 handling characteristics, 526–7 physical characteristics, 524–6 classification, 515–19 absorbable sutures, 515–18 non-absorbable sutures, 518–19 future trends, 531 history, 514–15 manufacturing process, 520–4 monofilament nylon suture, 528 size/gauge system, 519–20 stiff suture improper selection, 527 suture selection, 530–1 Surgilene, 519 sutures, 480–4 accessories, 523 braided suture showing less memory, 522 groupings, 515. ideal characteristics, 513 sterilisation, 523 synthetic polymeric monofilament suture manufacturing process, 521 see also surgical threads swaging, 520 swan neck, 64 Swicofil, 262 SWNT see single-walled nanotubes Sylramic, 360 synthetic fibres, 186 synthetic filament yarn, 226–9 T-measuring head, 250 tangling see commingling tape thread, 499 tape winding, 405
605
tape yarns, 6–7 applications, 52 production, 10–13, 11 controlled fibrillation, 12–13 fibrillated, 12 flat, 11–12 uncontrolled fibrillation, 12 properties, 44 Taslan nozzle, 402 Taslan process, 200 technical fibre characteristics, 39–43 absorption, 41 chemical and UV resistance, 43 mechanical properties, 39–41 thermal behaviour, 41–2 thermal conductivity, 42 technical sewing threads, 495–532 industrial sewing threads, 495–512 airbags, 510 antistatic safety workwear, 511 aramid threads, 506–7 automated multi-directional sewing threads, 502 carbon fibre threads, 508–9 fabrics and threads sizes, 501 finishing, 500 general properties of fibres used for sewing threads, 501–2 geotextiles, 511 numbering and packaging, 500–1 outdoor applications, 509–10 PTFE fibre thread, 507–8 structure, 496–9 ultra high modulus polyethylene threads, 508 various sewing threads in nonmedical technical applications, 511 very high temperature applications, 502–6 nonmedical applications, 512–13 selection chart, 501 sewing threads photographs, 497 surgical threads/sutures for medical applications, 513–32 characterisation, 524–30 classification, 515–19 future trends, 531 history, 514–15 manufacturing process, 520–4 size/gauge system, 519–20 suture selection, 530–1 thread packages, 501
© Woodhead Publishing Limited, 2010
606
Index
technical textile yarns accessing weavability, 215–30 evaluation, 223–6 importance in industrial fabrics, 216 influencing factors, 216–22 micro-denier yarns sizing for achieving desired weavability, 229–30 warp breakage mechanism, 221–2 warp breakage mechanism analysis, 223 yarn weavability, 215–16 applications, 48–53 core spun yarn, 52 monofilament yarn, 49–50 monofilament yarns products, 51 multifilament yarn, 50 multifilament yarns products, 51 plied and cabled yarn, 52–3 tape yarn, 52 used according to application or special properties, 49 characterisation, 26–32 different yarns packing coefficient, 31 dimensional parameters, 26–9 linear density units, 27 open and close packing, 30 packing of fibres, 29–30 specific volume, 28 twist, 30–2 twist direction, 31 unit conversion, 28 various parameters, 26 characteristics, 4–9 braided thread, 8 braided yarn, 8–9 cabled yarn, 8 classification according to raw material, 4 continuous filament yarn, 4–7 core spun yarn, 7 fibre cross-sectional shapes, 5 plied/folded yarn, 8 ply yarn and cord, 8 staple yarn, 7 classification on the basis of structure and form, 5 coatings, 140–83 choice of substrates, 162 coated yarns applications and properties, 176–82 formulations, 144
future trends, 182–3 knife coating, 170 methods and machinery, 170–6 polymers, 144–62 principles, 163–9 load elongation curves jute-polyester wrap yarn, 47 Kevlar and polyester cords, 48 market, 53 production, 9–26 braided yarn, 23–4 braiding process, 23 core spun filament yarn, 19 core spun Lycra yarn, 20 core-spun yarns, 18–20 fibrillation technique, 13 folded yarn, 20–2 friction spinning, 16 intermingled/commingled yarn, 22–3 intermingling jet, 23 melt spinning, 10 mono- and multifilament, 10 ring spinning process, 15 rotor spinning, 16 specialised yarns, 24–6 spinning process steps, 14 staple yarn, 13–17 tape yarn, 10–13, 11 wrap spinning, 18 properties, 43–7 cord yarns construction, 48 core spun yarn, 46–7 monofilament yarn, 43–4 multifilament yarn, 44 plied/corn yarn, 47 spun yarn, 44–5 tape yarn, 44 translation efficiency, 45 twist-strength relationship, 45 wrap spun yarn, 46 properties and performance, 37–43 fibre properties, 40 fibre resistance, 43 fibres thermal conductivity, 42 moisture regain and relative strength, 41 role of fibre parameters, 37–9 technical fibre characteristics, 39–43 structures modification bulking, 92–100 for functional applications, 91–110 future trends, 110
© Woodhead Publishing Limited, 2010
Index micropores incorporation, 100–2 twistless and hollow yarns, 102–9 textile coating and laminating, 141–4 uses of coated and laminated textiles, 142 twisted yarn structure, 32–7 equations showing relationship between parameters, 32 geometrical relations, 32–4 idealised helical yarn geometry, 33 plied yarn geometry, 35–7 yarn stress-strain relation, 34–5 types, 3–53, 4 Technora, 372, 375 aramid threads, 506 Teflon, 504 see also polytetrafluoroethylene Teijin, 372 Teijinconex, 377 Tenara, 499 Tenara M1000HTR, 509 Tenara M1000TR, 509 Tenara sewing threads, 508 tensilometer, 524 TephaFLEX absorbable suture, 531 Terylene, 157 Tester 5, 237 Tevdek, 518 Tex system of numbering, 500 textile yarn structures modification bulking, 92–100 bulked yarn production principles, 92–4 ring spun yarns, 94–6 staple fibre yarn, 93 yarns of different spinning technologies, 96–100 functional applications, 91–110 future trends, 110 micropores incorporation, 100–2 fabric characteristics, 101–2 micropores creation within the yarn body, 100 microporous yarn production principles, 100–1 yarn properties, 101 specific volume change after bulking core-sheath yarn, 98 yarns of different technologies, 97 stress-strain behaviour hollow yarn, 104 parent DREF-III yarn, 104 twistless yarn, 104
607
tenacity change after bulking core-sheath yarn, 99 yarns of different spinning technologies, 98 twistless and hollow yarns, 102–9 air permeability, 107 core-sheath type DREF-III yarn, 103 fabric properties, 105–9 mechanical properties, 106 production principles, 102–3 thermal resistance, 108 water absorbency, 109 water vapour permeability, 109 yarn properties, 104–5 textiles, 3 texture, 85 texturised yarns, 89 texturising, 85 see also yarn texturising TFBA see trifluoromethylbenzaldehyde thermal absorptivity, 186 thermal behaviour, 41–2 thermal conductivity, 42 thermal resistance, 108 thermo-mechanical process, 431 thermoforming, 425 thermophysiological wear comfort, 185 thermoplastic composites composite property relations, 413–20 hybrid yarns, 387–426 manufacture with hybrid yarns, 405–7 potential applications, 421–2 aircraft applications, 421 industrial applications, 421–2 trends in applications, 422–5 environmental issues and recyclability, 424–5 natural fibre reinforced thermoplastic composites, 422–4 thermoplastic melts, 388 thermoplastic polymers, 387 thermosetting matrix, 387 thermosetting polymers, 387 thermosetting resins, 388 Thornel fibre, 357 3D computer graphics and visualisation techniques, 568–84 CAD system descriptions for yarn and fancy yarn structures, 579–83 cloths and yarns, 570–2
© Woodhead Publishing Limited, 2010
608
Index
yarn and fancy yarn mathematical modelling, 573–9 yarn and fancy yarn microstructures, 573 computer-generated three-ply yarn, 574 cross-sectional profiling examples, 579 3D virtual reality cloth simulation, 571 grid system for woven fabric structure construction, 570 simulated plain weft knitted fabric, 572 simulated single-jersey jacquard weft knitted fabric, 572 three-ply yarn 3D double helix and twist structure, 575 3D photo-realistic models, 581 3D parametric tubes, 571 tissue drag, 525 tissue engineering, 484–7, 564–5 titanium dioxide, 272 toluene, 437, 548 Toray air-jet spinning, 71 Toray T300J carbon filament, 403 Torayca, 355–6, 357 Torayca T1000G, 347 torque, 39 Torque-Stop, 64 torsional rigidity, 39, 113 tortuosity, 34, 36 Towflex, 421 traveller, 14 trichloromethane, 540 trifluoromethylbenzaldehyde, 459 tripolyphosphate, 536 Tulsi, 287 turbostratic carbon fibres, 346 turning thread technique, 399 Twaron, 372 twist, 21–2, 30–2 fibrillation, 12 insertion, 63 twist jet fibrillation, 12 twist scale function, 577 twisted multifilament thread, 498 twisted yarn geometrical relations, 32–4 fibre-torsion and bending within yarn, 34 yarn contraction/extension due to twisting/untwisting, 34 structure, 32–7 plied yarn geometry, 35–7 yarn stress-strain relation, 34–5 twister-less method, 319
twistless spinning, 198–9 twistless yarns, 102–9 air permeability, 107 core-sheath type DREF-III yarn, 103 fabric properties, 105–9 mechanical properties, 106 production principles, 102–5 stress-strain behaviour, 104 thermal resistance, 108 water absorbency, 109 water vapour permeability, 109 yarn properties, 104–5 two-for-one twister, 21, 219 two-step melt spinning method, 539 Tyranno LOX-M, 360, 362 Tyranno SA, 360, 362 tyre cord yarn, 52–3 UHMWPE see ultrahigh molecular weight polyethylene ultra high modulus polyethylene threads, 508 ultrahigh molecular weight polyethylene, 378, 480 ultraviolet absorbers, 273 ultraviolet protected yarns, 266–73 preparation, 271–3 organic and inorganic blockers, 272 textile dyes, 272 ultraviolet protection factor, 268–9 factors affecting apparel textiles, 271 textiles classification, 270 ultraviolet radiation, 267 uncontrolled fibrillation, 12 UPF see ultraviolet protection factor US patent 4800113, 400 user interface module, 582 Uster, 249 Uster CAY, 252 Uster Quantum 2, 252 Uster Quantum Expert, 252 Uster Ring Expert, 252 Uster Slivergard, 251–2 Uster Tester 5, 244 Uster Tester 5-S800, 244 Uster Tester III, 118, 119, 121, 127, 130 Uster Tester IV, 118 Uster Tester 4SX, 238 Uster yarn hairiness tester, 118–19 vacuum coating, 166–7 VARIOdraft, 67 Vicryl, 516, 517
© Woodhead Publishing Limited, 2010
Index vinyl-coated fibreglass yarns, 179 vinylon, 554 viscose general properties, 502 spun thread, 497 steel-core threads, 506 viscosity average molecular weight, 539 visual processing, 233–4 visualisation module, 581 Viton, 154 void content, 410 volume data rendering method, 584 vortex spinning, 72–4, 198 core spun yarns production, 80 MJS and MVS working principle, 74 MVS vs MJS, 74 operation principle, 72–4 wales, 571 warp, 571 warp breakage mechanism, 221–2 analysis, 223 water absorbency, 109 water-retention value, 536 water vapour permeability, 108, 109 weavability assessment in technical yarns, 215–30 importance in industrial fabrics, 216 micro-denier yarns sizing for achieving desired weavability, 229–30 stresses on yarn due to loom actions, 221 warp breakage mechanism, 221–2 warp breakage mechanism analysis, 223 yarns, 215–16 evaluation, 223–6 empirical approach, 224 instrumental approach, 225–6 statistical approach, 224–5 failure mechanism single cold sized yarn, 222 single unsized yarn, 222 two-ply unsized yarns, 223 influencing factors, 216–21 loom actions and conditions, 220–1 yarn preparation, 219–20 yarn quality, 217–19 synthetic filament yarn, 226–9 breakage mechanism, 228 evaluation of sized filament yarn, 227–9
609
filament warp preparation, 227 sized filament yarn evaluation, 227–9 weaving, 122–3 weft, 571 Weibull distribution, 224–5 wet spinning, 24–5 equipment schematic diagram, 436 shape memory polymer yarns manufacture, 435–6 wicking, 108 wire sutures, 523 wood flour, 561 wool, 42, 185, 187 spun thread, 497 Woolite, 281 woollen spinning, 189–90 woollen yarns, 189 worsted spinning, 189–90 worsted yarns, 189–90 wound dressings, 469–70 wrap-core-wrap sandwich, 75 wrap spinning, 18, 80–2, 197–8, 393 operation principle, 80–2 wrapping system and filament wrapped yarn structure, 394 wrap spun yarns, 81, 197 jute–polyester wrap yarn load– elongation curves, 47 properties, 46 Yardage Controller, 72 yarn characterisation, 236–45 commercially available testers, 243–5 computer vision for textured yarn interlacements, 241–2 hairiness, 240 image processing to control nanofibre production, 242–3 irregularity measurement, 238–40 state of the art, 236–8 system quality, 241 system to control textured yarn interlace, 242 yarn connecting unit, 79 yarn hairiness, 216, 218 compact and spun yarns different counts, 130 different twist levels, 130 effect of test speed 18 tex rotor yarns, 121 worsted yarns, 121 fibre-related factors, 113–14
© Woodhead Publishing Limited, 2010
610
Index
fibre fineness, 114 fibre length and short fibre content, 113 torsional and flexural rigidities, 113 importance, 122–5 effect in spinning, 122 effect in weaving and knitting, 122–4 effect on fabric properties, 124–5 effect on weft velocity profile in airjet weaving, 123 influencing factors, 113–17 measurement, 117–21, 240 results correlation, 120 results from different instruments, 119–20 Shirley yarn hairiness tester, 117 testing parameters effect, 120–1 Uster yarn hairiness tester, 118–19 Zweigle yarn hairiness tester, 118 modelling, 125–8 ANN prediction performance and regression models, 127, 128 artificial neural network modelling, 126–8 mathematical and statistical models, 125–6 simple artificial neural network model, 126 process-related factors, 114–17 blending and mixing parameters, 115 combing operation, 115 number of drawframe passages, 115–16 roving fineness and twist, 116 spacer size, 115, 117 spindle speed, 116 spinning draft, 116 spinning technology, 114–15 traveller weight, 117 winding operation, 115 yarn twist, 116 reduction, 112–37 average S3 values per 100 m yarn, 137 compact spinning technology, 128–30 effect of jet-winding parameters, 134 jet-ring spinning system, 131–2 jet-winding or nozzle winding system, 132–5
left and right diagonal arrangements, 136 modified yarn path in ring spinning, 135–6 spinning triangles, 129 yarn imaging advances in yarn characteristics measurement, 232–54 future trends, 254 computer measuring system block scheme, 251 concept of image, 232 digital image processing, 234–5 system, 234 image classification, 233 image processing in industrial processes, 233–4 image processing techniques, 235–6 digital image processing in fibrous material structures, 235–6 fibrous materials structures, 235 online systems for measuring yarn quality, 247–54 commercially available devices, 251–4 state of the art online systems, 247, 249–54 special advances in measuring yarn characteristics, 245–7 macro- and micro-level tests, 247 potential causes for defects, 248 quality inspection methods for manmade fibres, 246 yarn quality in the spinning process, 246 yarn characterisation, 236–45 commercially available testers, 243–5 computer vision for textured yarn interlacements, 241–2 hairiness, 240 image processing to control nanofibre production, 242–3 irregularity measurement, 238–40 measurement of hairiness, 240 optical and capacitive methods, 239 state of the art, 236–8 system quality, 241 system to control textured yarn interlace, 242 thick and thin points, 238 yarn irregularity, 238–40 yarn quality, 217–19
© Woodhead Publishing Limited, 2010
Index
abrasion resistance, 218 classimat faults, 218–19 commercially available devices for measurement, 251–4 Barco solutions, 253–4 Uster solutions, 251–2 count strength product, 217 hairiness, 218 online systems for measurement, 247–54 state of the art, 247–51 single yarn elongation, 217–18 single yarn strength, 217 system quality schematic, 251 yarn spinning advances, 56–89 future trends, 89 introduction to various technologies, 56–7 air-jet spinning, 70–2 latest developments, 72 Murata jet spinner principle, 71 operation principle, 70–1 compact spinning, 57–61 Air-Com-Tex 700 process, 60 ComforSpin process, 58–9 EliTe spinning, 59–60 RoCos compact spinning, 60–1 yarn formation in ring spinning and Comfor spinning, 57 core spun yarns production air-jet/vortex spinning, 80 friction spinning, 80 ring spinning, 75–6 rotor spinning, 76–7, 79 core yarn spinning, 74–80 ARS filament-core spinning system, 75 core-spun yarns and fabrics details, 78 Rotona core spun yarn structure, 79 Rotona process, 79 staple core yarn spinning schematic, 77 vortex-spun and ring-spun core yarns structure, 80 developing particular yarn properties, 82–4 applications, 84 fibre properties, 84 friction spun yarns technical applications, 85 raw materials used, 83
611
role of process parameters, 83–4 role of raw materials, 83 specific applications, 84 friction spinning, 67–70 DREF 2 friction spinner, 68 DREF 3 friction spinner, 69 DREF 2000 friction spinner, 70 latest developments, 69–70 operation principle, 67–9 rotor spinning, 61–7 latest developments, 63–7 operation principle, 61–3 SC 1-M and SC 2-M spinboxes benefits, 65 vortex spinning, 72–4 MJS and MVS working principle, 74 MVS vs MJS, 74 operation principle, 72–4 wrap spinning, 80–2 operation principle, 80–2 Parafil wrap spinning, 81 wrap spun yarn structure, 82 yarn system quality, 241, 250–1 yarn tension, 250 yarn texturising developments, 86–9 air-jet texturising, 87–9 BCF process schematic, 88 bulked continuous filament process, 88–9 false-twist texturising, 86–7 prominent technologies, 85–6 air-jet texturising, 86 false twist texturising, 86 technologies developments and applications, 85–9 technical applications, 89 yarns bulking of yarns of different spinning technology, 96–100 fabric characteristics, 99–100 specific volume change, 97 tenacity change, 98 yarn characteristics, 97–9 design using 3D computer graphics and visualisation techniques, 568–84 specialised yarns production, 24–6 coating/dyeing, 25 conducting yarn, 24 core spinning technology, 25–6 melt and wet spinning, 24–5 spun yarn technology, 25
© Woodhead Publishing Limited, 2010
612
Index
Yasuda parameter, 467 Young’s modulus, 347 YSQ see yarn system quality Z-twist, 31 Zari, 273 zero-twist staple yarn, 198
zinc oxide, 273 zirconia, 365 ZT 5, 243, 244 Zweigle G565 tester, 119, 130 Zweigle G566 tester, 114 Zweigle yarn hairiness tester, 118 Zweigle’s Multitester, 243–4
© Woodhead Publishing Limited, 2010
